Jump down this page to:
Startup Issues and Errors
Hangs and Unresponsive apps
Communications, eMail Problems
Printers and Peripherals
Kernel Panics ("You need to restart...")

Check your Hard Drive:
Find your Hard Drive icon on your desktop (should be in top-right corner), select it with one click (only), then choose "Get Info" from the Finder's File Menu.

The resulting window shows Hard Drive capacity, space available and used space. If available space is getting down to 10-15% of drive capacity, your drive is full; less than 10% means trouble is brewing.....

About This Mac:
Properly identify your machine by collecting its system specifications and details. Just ask your Mac:

Select "About This Mac" under the Finder's Apple Menu; here you'll find OS version number, details regarding your machine's processor(s), installed RAM information, and info about your startup (or boot) volume.

Much more complete and detailed specs may be found in the System Profile (click More Info button in the "About..." window). Here you'll find most anything you might want to know about your Mac's hardware and software.

System Profile:
Illustrated here is System Profile's Memory pane showing specifications on each installed memory module in each available slot. Equally detailed and specific information is also available for every drive, card, bus, port, and device. If you use a notebook, you'll also find battery and charging status under "Power."

Serial Number:

All Macs have their serial numbers recorded under "Hardware" at the top of the System Profile window (where it may be easily read and copied). Serial number and specs may also be found on back of notebooks in wee-tiny print, or on a label inside battery bay of older laptops with removable batteries. iMacs have serial number and machine specs on underside of stand, towers have a label under side door or on back panel.  The serial number may be used to ascertain warranty status and further identify machine specs.

Model Number:
For some inexplicable reason, Mac model numbers are seldom used to identify machines, even tho every model has one. Machines are best identified by specs on their labels or in System Profile, or by serial number.

Start with an overall examination. Take nothing for granted.
It might be a good idea to take notes as you go through the inspection process. Some steps may seem unnecessary, but try 'em anyway, just in case. Be methodical.

Power down. Disconnect power to CPU and all components.

Two reasons for this: First, it eliminates any possibility of damage that might be caused by disconnecting/reconnecting powered devices. Second, removing power from computer and all components for a minute or so (including printer, modem, router, and all peripherals) will cause some devices to reset when powered on again, thus eliminating a few possibilities right off the bat. Test and confirm power from outlets on any surge suppressors or power supplies (UPS) in use and/or bypass these.

One-by-one: Disconnect, examine, reconnect each cable.
While things are shut off, take a good look at all cables, cable ends and ports. Are contacts clean and shiny, or are they dirty, dull and oxidized? Are connectors in good shape and intact? Damaged cables should be replaced; damaged ports may be another matter. If necessary, carefully clean connectors, blow out ports and plugs, then reconnect each device cable. Make sure plugs have a snug fit and cables aren't being strained, twisted or bent.

If a new device has been added recently - including any internal cards - remove it and leave that device aside for now. (Hardware problems often manifest themselves during startup, causing freezes, hangs and/or blank screens.)

Reconnect power to peripheral devices.
Turn on each peripheral and allow time for printers, modems, routers (etc.) to go thru their startup routines. When all external devices are up and running (typically a minute or two), reconnect power to the computer and turn it on. If problem remains, shutdown your computer, disconnect power and replace/reconnect cards/devices one-by-one, testing startup with each. If problem reoccurs, the last connected card/device might be at fault.

If problem never went away or startup to (desktop) is impossible, the next steps will be unavailable and you might want to bring machine in.

Check System Prefs (if possible).
If you startup to a date/time error message, your desktop computer's PRAM battery is probably dead. (Some older machines may refuse to boot at all with a dead PRAM battery.) Replacement batteries are readily available but may require partial disassembly for access. (Notebooks have something more like a capacitor than a battery, and an overnight charge will refresh most notebook PRAM batteries.) Now might be a good time to consult your user manual, too.

Open System Preferences and check settings in relevant control panels and panes. Be sure to check the Accounts pane -> Login Items (or Startup Items) and make sure there isn't something launching on startup that might be the culprit. NOTE: Now is not the time to change anything other than those settings that may be related to the specific problem you are experiencing; you're likely to see login items installed by your OS (iTunes, for example) that should remain. Third-party (non-Apple) items are always suspect, especially auto-update daemons.

Try to isolate and identify the problem.
Record any error messages that appear. Is the problem repeatable? What action or event preceded the problem? Does it seem to be related to a specific application? If so, check the program's preferences (usually under the Application or Edit menu).

If problem appears to be related to a peripheral device - printer, scanner, modem, router, etc. - make sure any suspect device driver is current by checking its version numbers and system requirements. (Drivers on CDs included with most devices may be unnecessary for use with Macintosh, or they may be already be outdated at time of purchase.) If you've done an OS upgrade, you may need to download/update your device drivers, too.

Collect System Info.
The first item under the Finder's Apple menu is "About This Mac" and will identify your Operating System version, processor info and installed RAM.
Copy down info and identifiers as it applies to the problem at hand. See "Collecting System Info" section (top of this page) for details on where to look and what to look for.

Before you call for help:
Regardless of where you might turn for assistance, you'll save yourself time and trouble by having the following information readily available (and tech support doesn't come cheap):
  • Machine type (notebook, iMac or tower), processor type and speed (XX.XGHz WhatsitCPU), OS version number, and installed RAM. Hard drive capacity and available (free) space might be helpful, too.
  • Changes or events related to the issue, especially anything recent, and specs for any peripherals involved.
  • A record of error messages, symptoms encountered, and steps taken.
The amount of relevant information you have on hand when you call tech support will determine a lot of your success in receiving help. From a tech's point of view, it's much easier to have a coherent conversation when both parties know what equipment is in use, under which Operating System, and exactly what error messages or symptoms are being generated, when, where, and under what circumstances.

If your Mac is under warranty, you may be entitled to free tech support - check your warranty info (also available by serial number from Apple's support page found here under Apple links). Most hardware/software vendors charge for phone/online support by incident or by the minute. We don't provide free tech support, either. In fact, it's rare to diagnose a problem over the phone, let alone solve it, so we respectfully request you bring your machine to the shop for a proper diagnostic evaluation. See our Service Policies and Ops page for details.

Oooo, pretty!
First, be patient; the beachball cursor is there to indicate machine is busy. But, if it seems stuck after awhile, there's a "Force Quit..." command under the Apple (logo) menu that should get you out of it. If that's not an option, you might have to force shutdown by pressing/holding power button for 6+ seconds which will end a hang and shutdown machine - but does nothing to prevent it from happening again under same circumstances (unless it was just a fluke). If you want to prevent beachballs in the future, or you find it's happening far too often, then something needs to change.

And the cause is...?
Common software causes (with easy fixes) include:
  • A cluttered desktop littered with folders full of pics or music or videos, misplaced apps and huge downloads can slow things down. File things where they belong - in the drive - and clean up that desktop. Empty the trash.
  • Using 'List View' with file size displayed. Use Column View instead (Finder > View menu) or, if you prefer List View, uncheck "Size" under View Options at bottom of the Finder's View menu.
  • Running too many apps at once. Closing windows does not quit an application; when you're done with an app, choose "Quit" from the app's menu or press Command+Q on the keyboard.
  • Unnecessary anti-virus and utility apps. Anti-virus apps insert themselves into practically everything you do, and will slow things to a crawl with little or no benefit. Legitimate AV programs will have an uninstaller attached - use it.
"Slow" is a pretty vague complaint, helps to know if it's related to a particular program - web browsers for example. Browsers collect a lot of so-called "cruft" these days, a term encompassing cookies, history, location info, icons, autofill and other web data. Safari has a Reset function conveniently located in the Safari menu that can clear out most of it with one click, a good habit to get into these days when quitting Safari. (Other browsers have similar functions typically buried under their preference settings.) If machine slowness is system-wide and not limited to a particular app, a little more investigation is required but it can usually be sorted out quickly here on the bench.

More complex causes, including downloads:
Utilities and trouble-shooting apps can do more harm than good when installed and run unnecessarily or improperly. Purloined programs downloaded from suspect sources (torrent or "file-sharing" sites) are always suspect and frequently cause trouble - which is to be expected - but there are also some apps around that are just plain nasty. One prime example is MacKeeper, an insidious scam from an unscrupulous vendor that can be very difficult to remove. If you were unfortunate enough to download and install any version of MacKeeper, this link may help you lose it and get your Mac back: Applehelpwriter.com. MacKeeper's uninstall process leaves some files behind that can tie-up the CPU by throwing relentless errors, thereby creating the very problem it pretends to solve. Intentional? You might think so if you saw it in action.

There are some great utilities out there that actually do what they're supposed to do, many of which are typically little more than a nice user interface applied to UNIX functions built into your OS (no harm in making maintenance routines more user-friendly). Cocktail is a great, simple "cleanup" utility as is OnyX, TinkerTool is also excellent and has lots of functions and options and monitoring apps. If you feel you _must_ install anti-virus software, ClamXav comes highly recommended, but be aware that any anti-virus app will slow operations as it performs scans and executes its duties.

Hardware: How much memory (RAM) is installed?
In ballpark numbers, 1-2GB RAM is barely adequate these days, and 2GB is minimum requirement for OS 10.7/10.8/10.9. (See Collecting Specs, above.) RAM is working space, and if the OS is taking it all, there won't be any left for other apps to use. If you upgrade your software/OS, be sure to check RAM requirements and upgrade accordingly. Freezes may be caused by an application running out of memory, or too many apps running simultaneously. (Polite apps might warn you before they run out of memory, but don't count on it.) Amount of RAM required depends on what you use your computer for, of course, and some apps require much more RAM than others. Check your Dock and quit the apps you're not using. Or maybe it's time to restart?

Other possible causes related to slow, unresponsive Macs include failing hard drives, corrupt (damaged) or missing System segments, wacky application software, optical drives or peripherals gone wild, and a whole slew of other things. A damaged input device can mimic a freeze, too. Bring it in and we'll figure out what's slowing things down.

Check System Prefs > Network, and Mail.app prefs.
Possibly the most common complaint comes from people who suddenly are unable to send and/or receive email. The problem might well be on your server's end, especially if none of your machine's settings have been changed, all cables and devices are intact - and you're in Nevada County. If it just keeps asking for your password, and you haven't changed anything, the problem is probably not on your end. Sometimes all you can do is wait a day or so and try again. A lot of changes are going on with ISPs, too, as they begin to meter data transmission, throttle bandwidth and calculate extra charges for connected devices. The better ISPs out there post system status bulletins on their web sites (if you can get online). Lesser ISPs like Ma Bell and Comcast should have phone numbers on their bills for outage and status info. Good luck w'that.

An enormously helpful Apple Mail support page may be found here: Mail.

It's important to make the distinction between ISPs and ESPs:
Internet Service Providers (ISPs) = Comcast, ATT, Cox, Hughes, Wildblue, etcetera; these are cable, phone, satellite and microwave companies.
Email Service Providers (ESPs) = Yahoo, Google, Hotmail, et al.
If you can't get online at all, it might be your ISP. If you can't get mail, it might be either. Try web mail: Launch a browser (Safari), go to ESP's server and login to your mail. That might narrow things down.

If you're on a wireless (AirPort or WiFi) network, your AP menu and/or Network pane in System Preferences should show name and status of your selected network. If so, your Mac and router are communicating and the problem is somewhere between router, modem and ISP. If you use a notebook, take it out on the town and try connecting to a different network at a coffee house or a friend's location. Might be a good time to write down the settings you see, too (port numbers, SSL on/off, DNS numbers, etc.), but don't change anything unless you know what you're doing(!).

Modems sometimes fail, as do routers, and most have lights indicating status. A damaged modem may report any number of odd (sometimes misleading) errors, it may endlessly try to connect or disconnect, its power supply may have failed, or your network prefs pane may insist that there is no device connected. Try resetting both modem and router (no harm in doing this):
  • Shutdown your computer and remove power (unplug) modem, router and/or gateway. Take a moment to check all other cables/connections.
  • Wait a minute or two, then reconnect power to modem, then to the router. After these gizmos have completed their startup routines (about a minute or so), cross your fingers and startup your Mac.
  • If communications have been restored, you're good to go.
  • If not, and you haven't changed any email send/receive or username/password settings, then either your ISP is temporarily offline or there might be a hardware/software issue that needs further evaluation.

Make sure all connections are intact and power is on.
Sometimes it helps to power-up printers and peripherals _before_ starting up your computer. Check printer's ink tanks or cartridge. Look for any physical damage to the device, its cables and ports, make sure everything is properly connected. Power up peripherals, wait a minute or so, then power on your computer. Check settings; make sure your printer appears in Printer List (System Prefs -> Printer and Fax -> Setup), make sure external drives and devices are mounted and functional.

If printer is producing distorted output (too small or too large, sideways, missing fonts or styles), check Page Layout settings (in File menu) in the application you are printing from. If output appears as a page of gibberish, or machine spews out blank pages along with the desired job, or output problem persists, try printing something from a different application. For example, launch TextEdit, type something, and see if that prints properly. If so, the problem is app-specific. If not, your printer (and/or its driver) is at fault. If you've recently upgraded your OS, you may need to download and install or update to a newer driver. (Same may be true of scanners and other devices.) Consult your printer's manual and try running printer's self-test to see if the printer itself is malfunctioning.

If you are trying to print a page from some web site, know that web pages are not necessarily designed to be printed and printer output might be spread over multiple pages in ways you wouldn't expect, or you may only be able to print a portion of the page's layout due to frames, tables and other design elements. There are workarounds for this - but don't blame your printer.

Sometimes there's just nothing to do.
This message appeared one day for no apparent reason, with no workaround. Tried every way possible to save this document - Photoshop simply refused access to anything, no matter what. Sure, blame it on the disk. And no, it's certainly not OK.

Check and fine-tune your System-wide settings.
Adjustments in System Preferences will frequently solve display "problems," while various view options (including those in Finder's View menu and Finder Preferences). Some commands can show or hide controls, so sometimes you need to make controls available in order to change them.

Clockwise from top: Disk Utility, Finder Prefs, System Prefs, and Get Info windows from OSX

Review System Preferences:
Your System Preferences control the appearance and operation of your machine's Operating System. System Prefs are available from the Apple menu and from its icon in the Dock at the edge of your screen (both illustrated at right).

Accounts, date/time, desktop color/image and screen saver options, Dock settings, network settings (email and internet), printer, keyboard and mouse, startup disk and most other controls are located in System Prefs. Each of these controls can be changed and customized to suite each user; settings are specific to each user account.

By the Way, while we're on the subject...
Many people think clicking a close button in a window's top-left corner () is the same as quitting the application. It isn't. It merely closes the window (in most cases), leaving the application open, active and running. Why is this important? Because applications load into memory (RAM) when launched, and quitting unused applications frees up precious RAM. Instead of clicking the close box when finished with an application, choose Quit from the File menu, or type Command+Q.

(Having said that, I should point out an inconsistency with the close button: Sometimes it _does_ cause an app to quit in addition to closing a window, as is the case with System Preferences and a few other System-related windows. Just make sure you quit apps when finished with 'em.)

Run Disk Utility periodically.
Inside Applications -> Utilities folder is the Disk Utility application. Running Disk Utility to verify your hard drive and repair permissions can fix many minor errors before they become bigger issues.

Check PRAM Battery (aka "backup" or "clock" battery):

If your desktop Mac is 5-years-old or more, its internal battery may be getting weak. Symptoms include a date/time error on startup, preference settings that may revert to defaults, and possible startup issues (very rare). Older Mac desktop machines use a 3.6v, half-AA-size lithium battery, while newer Macs have a 3v CR2032 button battery. Replacing a battery is an easy do-it-yourself fix for tower machines (PowerMacs and Mac Pros), just make sure to note polarity when removing old battery.

iMacs require disassembly and some expertise to access the battery - the newer the machine, the more difficult it is to replace its battery. If your iMac has an aluminum case, it requires removal of glass face and display screen to access the PRAM battery. Real new models (those lacking CD/DVD drives) may use adhesive to secure glass, making access even more difficult. Check your user manual or look your machine up online to see what's involved regarding your specific model.

Notebook Macs don't have PRAM batteries as such; they rely on machine's main battery to maintain settings (incl. date/time). Older laptops may have a capacitor instead of a PRAM battery (so that main battery can be removed and replaced without losing settings), but new MacBooks don't even have capacitors. Instead, Apple has decided to prevent battery removal altogether by placing it behind bottom case and securing it with tamper-proof fasteners or adhesive.

Fan noise and/or excessive heat:

Desktop or laptop, all computers have fans in them these days because their processors typically run at 140-150F or more. And they all collect dust eventually.

This photo shows a removed fan from a MacBook Pro and the dust it left behind. Fan's exhaust vent is almost completely blocked with a half-inch buildup in right corner. Those fins carry heat from machine's heatsink to the fan, but they can also catch any fuzz from blankets, pets or clothing that may happen to pass by. Whenever any machine gets disassembled here at the shop for any reason - desktop, tower or laptop - we thoroughly clean fans, vents and interior because they all get dusty over time, and a good cleaning can add years to a machine's life. In this case, the fan itself began to make noise and had to be replaced.

All Macs have sensors within them to protect machine from overheating. You may get a warning - or not - but machine will put itself to sleep if it senses an overtemp condition, and/or shut itself off if necessary. Fans will ramp-up as needed, usually running at idle speeds during normal use, but when they go full-tilt you'll certainly hear them. If your Mac is making noise, getting abnormally hot or fans are running at high-speed all the time, it may be due for a cleaning.

Clear web browser cache:
Safari has a simple and convenient menu item that empties Safari's cache (right), and another menu command just above it - Reset Safari - that will clear a slew or other records and settings, including history, auto-fill and every other modification made to Safari (except bookmarks), setting it back to its original, unused state.

Firefox and other browsers also allow you to clear the cache, but the command is typically buried somewhere in browser preferences and can be hard to find.

Clean out old emails:
We've seen mail apps so stuffed with old email - including unemptied trash and spam - that messages number in the tens of thousands. Nobody has time to sort thru all that. Get rid of it! Clear out that inbox, empty the trash, delete all that spam. Your inbox should be kept empty, with incoming emails either deleted, saved to a mail folder, or otherwise dealt with every time you retrieve new email.

Archive old mail you wish to keep:
If you like, you can collect and export old emails from Mail to a TextEdit file, including email photos, graphics and live links. Here's how:
First, select the messages you wish to save; the idea is to get them all into a single group, so you might want to create a Mail folder to contain them, then drag messages into the new folder. Select all messages by clicking the first one, scroll down to the last message, hold down Shift key and click last message.
With all messages selected, choose "Save As..." in Mail's File menu. From the resulting dialog box (right) give the file a name, select a destination, and be sure to save in Rich Text Format (to preserve links), then check the "Include Attachments" box to preserve all images and attachments - inline - with your messages.

Five easy reasons to clean up those files:
  1. Your primary hard drive - or boot volume, if you prefer - requires a certain amount of free space to run efficiently. Deleting unused/unwanted files frees up space for file and volume optimization processes to take place. A crowded, near-full hard drive will be sluggish; a full drive will eventually refuse to even startup.
  2. Searching thru organized files is easy. When you save a file, pay close attention to where it is going, and be sure to send it into the proper folder where it belongs. Whatever scheme you use to sort and organize things is fine, as long as it works for you. The Operating System creates a Home Folder for each user, along with root-level folders for Applications, Documents, Music, Pictures, Movies and the like, and that's a good place to start.
  3. A neat, well-organized drive makes for a neat, well-organized backup. Get all that junk off your desktop or you'll be seeing double when you mount your backup drive (duh!). Empty trash (including email and browser cache), run Disk Utility's First Aid now and then. You _do_ have a backup plan in place, right?
  4. A nicely organized drive lends itself well to customization. A nice desktop photo and screen saver, custom window colors and fonts..... Since you'll be creating special folders to hold special files, why not create custom folder icons while you're at it? If you're creative and resourceful enough, have at it. Google "custom OSX icons" for ideas and custom icons if you like.
  5. If a drive fails - Heaven forbid! - a tech will have a much better chance of recovering your data if your files are well organized and properly stored under named Admin accounts. Directories get overrun, drives go wonky, video and music and photo libraries grow at alarming rates, things can ugly in a hurry. Good thing you have a backup, huh. (Hint.)
UNIX maintenance routines:
If you leave your computer running day and night, automated maintenance routines will run periodically - daily, weekly and monthly - as they are designed to do (usually in the wee hours of the morning). If not, and you are familiar with the Terminal application, you probably know the commands to execute these routines, bit if you're like most Mac users you'll want a graphical interface to these commands. A few recommended utilities are listed below. Some of these also include a few additional System tweaks and tricks. NOTE: Be sure to match utility version to your OS version.

Startup problems.
Startup issues are best handled by exploring all the easy solutions before moving on to more complicated suspects. Start with status of the boot volume. If it's a notebook, has it been dropped or damaged? Will it boot from your OS disc or Lion flash drive?

Reading Symptoms:
Simple as it may sound, failure on startup arrives in a variety of ways with a variety of symptoms (and clues). Try to answer these questions:
  • Did you hear the normal startup sound? No sound (is sound turned down or off)? A different sound, a tone or beeps perhaps? How many beeps?
  • Does the power button light up? Does it stay on or go off when released? Is it pulsing? Does any sound at all come from the CPU (fans, drives spinning, other noises)?
  • Does an icon appear onscreen? If so, what does it look like? If it hangs, what's on the screen? Is the screen black, blue, or gray? What is the cursor doing? Do you get a message saying that you need to restart in four languages? (If so, sorry. See Kernel Panics, below.....)
  • How far do you get? Nowhere (black screen), to the Apple logo, to a blank gray, white or blue screen, to the desktop? What's on the desktop, what's in the menu bar? Anything launching on startup/login?
If you've checked all the usual suspects and machine still refuses to boot, try starting up from your (OS-version appropriate <-important!) System DVD:
  • Insert your System Install CD/DVD into the optical drive.
  • If machine is on, shutdown (hold power button down for 5 seconds).
  • Sometimes waiting 5-10 minutes with power disconnected helps.
  • Startup from optical drive by pressing "C" key during startup.
  • When you arrive at the Installer, ignore it and launch Disk Utility from the menu bar.
  • Select your hard disk in DU's window and run Disk Repair function.
  • If repairs complete successfully, restart. You're all done!
  • If you're stuck, call for an appointment and bring it on in.....
Set your Startup Disk (in System Preferences):
If your startup volume is not specified in your System Prefs, your Mac may take quite awhile to startup as it searches all connected volumes for an OS; check your Startup Disk setting and make sure the proper volume is selected (as illustrated below).

Some machines will not boot at all without a specified volume. If this applies to you, boot from (version-appropriate) System disc (hold "C" key during startup with bootable disk in drive), and set startup disk from the menu command.

Pay special attention to the Operating System:
Having more than one Operating System per volume is not a good idea. In fact, it can be a disaster. (The lone exception, of course, was OSX + OS9 Classic Mode.)

Even if Disk Utilities passes all tests, various hardware tests pass, everything comes up OK, doesn't mean your Operating System is undamaged; a battered OS can certainly prevent normal startup but might not produce errors in Disk Utility. Before doing anything drastic (like replacing your OS) and running the risk of making matters worse, call for an appointment and bring it in!

The dreaded Kernel Panic (KP).
With instructions to restart in four languages, a Kernel Panic doesn't give you any other choice. Sometimes, a restart is, in fact, all that is needed and things will return to normal. If it appears again after a restart, something more serious has gone wrong.

Before putting yourself (and your Mac) thru the trials listed below, you might save yourself the trouble of trying to deal with a KP yourself and bring the machine to our shop for service. Having said that, presented below - for information purposes only - are a few basic steps toward diagnosing possible causes of a Kernel Panic. What follows is a brief test using System install DVD that came with your computer or was used to upgrade (up to OS 10.6.x), or using the recovery partition (OS 10.7 and later).

First, shut off computer and disconnect all attached devices. Then startup machine and see the KP has gone away. Yes = suspect external device, no = internal problem. Normal troubleshooting routines start by checking simple things first in search of a quick fix, but troubleshooting Kernel Panics is a little different. By eliminating connected hardware components, we are eliminating them as possible causes. They can be reconnected, one at a time, and tested individually if KP is solved without them.

IMPORTANT: Do not attempt to make repairs from any software older than your Operating System. Newer utilities should be okay, but anything older than your OS will likely fail or may do damage.

10.6 and earlier Systems: Startup from the OS DVD used to install your OS and run Disk Utility on your hard drive. It's worth saying again: At the first hint of any trouble, run Disk Utility to check hard disk and repair permissions, if possible. If disk repair is necessary, you'll have to boot from OS DVD in order to repair your hard drive.

10.7 and later: Press and hold Option key immediately on powering on and select recovery partition for startup. Then run Disk Utility on your hard drive from recovery partition.

KPs in general:
These can be indicative of both hardware and software problems, making them rather difficult to troubleshoot. One possible cause is defective or failed memory (RAM). Other causes include damaged ports, connectors, and peripheral devices; failed, failing or corrupt hard drives; and failed or damaged video cards, cables/connections, or -worst case - logic boards.

If hardware is not the cause, other suspects include corrupt, damaged or missing Operating System, firmware issues, device drivers, corrupt fonts, and incompatible application programs. The list goes on and on.....

KP while running, versus KP on startup:
The timing of a KP's appearance can be a significant clue as to its cause. If KPs appear during the course of operation, it might be connected to use of a particular application, a specific OS component, or a device driver. If so, uninstalling and/or reinstalling (or updating) the suspect software might return your machine to normal. If you're not sure about deleting things, don't. You can temporarily move a file to the trash and thereby deactivate it on restart - without emptying the trash and actually deleting it. Just make a note of file's original location so that it can be returned to its proper location later.

If a KP appears on startup - on each and every startup - the problem is probably more serious. It might still be a software issue of some nature, but more often than not it will turn out to be hardware related.

Recent changes might suggest cause.
With so many potential causes, it might be helpful to recall events immediately preceding the appearance of a Kernel Panic. Any recent changes, additions or hardware/software installations may have been the cause; KPs might not appear until your next startup, so go back to the last change that was made before shutdown.

Run Apple Hardware Test (up to OS 10.6).
Try booting from Apple Hardware Test (AHT) located on disk 1 of the DVDs that came with your Mac (up to OS 10.6 - AHT is unavailable for later versions): Insert disk 1, and startup while holding down the "D" key, or use Option key (Startup Manager), select AHT and continue startup. With some OS versions, AHT is on a separate (usually silver) disc that will have "AHT" printed on its label. Examine contents of the System Profile tab to make sure all devices are properly identified. Next, run the Quick Test. If the Quick Test turns up nothing, try the Extended Test; if no error is produced, you might try letting it loop a few times. AHT may indicate a hardware issue, but it does not test software.

If all tests pass without error, and all hardware is properly identified, that - sadly - does not mean everything is A-OK. We've had machines refuse to boot from anything _except_ AHT (including the OS Install disc) but all AHT tests passed with flying colors anyway.