Here is a compendium of trouble shooting techniques for Macs. See my Repair Stories page for some descriptions of problem solving.
You should have been doing regular backups, so that even if you have trouble, you won't lose your files.
To report a problem, write down:
Do not guess about why it didn't work. Experts are often wrong; beginners even more often. Don't mix speculation with facts: it wastes everybody's time.
If you have a program that crashes or fails when you run it:
If you are having an Internet problem, for example if there is "connection failure" or a little exclamation in a triangle next to Inbox when reading mail, or the web browser displays a "can't connect" message:
If an application will not respond, won't drop its menus, or you can't quit it, try holding down Command and Option and hitting ESC. Then select the application that won't quit. Killing an application this way will lose all its unsaved changes. It is a good idea to get in the habit of doing a Save often, especially if you are having problems with apps like Microsoft Word. If you can copy the whole document before killing the application, maybe you can save your content.
Sometimes everything gets stuck: the cursor may not move when you move the mouse or trackpad; you can't change applications even with Command-Tab. To shut down your computer, hold down the Power button for about 10 seconds. The screen should go black. Then press Power once and the computer should restart: it may take longer than usual to reboot, because it is checking your file system and fixing errors.
Sometimes the Mac operating system gets screwed up. One thing to try is restarting: select. This will tell all applications to quit, reset the hardware, load a fresh copy of the operating system, and reinitialize the OS tables. If your computer is completely frozen and won't restart, hold down the power switch for 10 seconds to force a crash (this loses unsaved work).
If your computer crashes every time you start it, try to restart it in safe mode. Hold down the shift key and start. Keep holding down the shift key until the desktop is displayed.
Rarely, it will happen that the hardware's Parameter RAM (PRAM) is corrupted. This little bit of memory holds a few values used by the OS while the machine is off. You can "zap" (that is, reset) the PRAM by restarting while holding down Command-option-p-r. (This may not work from a wireless keyboard.) The computer should chime, then chime again. I had to do this when my MacBook Pro wouldn't display anything after it woke from sleep. After you zap the PRAM, the machine will forget how loud you had set the system sounds.
Rarely, your computer's System Management Controller will get confused. This chip controls noticing lid opening and closing, display backlighting, display selection, fan speed, and other hardware related functions. Put the machine to sleep and wake it, and do a restart, before resetting the SMC. Directions for resetting it depend on what kind of Mac you have. For a Mini, you unplug all peripherals and the power, then hold the power button for 10 seconds. For some laptops, you take out the battery.
Older PowerPC Macs have a Power Management Unit (PMU) instead, and the reset procedure is different. Use Google to find procedures for your machine model.
Hardware problems are very rare, but when they happen, your computer may behave inconsistently and fail in strange ways. It may be a good idea to rule out failing hardware by running the diagnostic programs that came with the machine. Find the original boot disc that came with the computer and put it into the CD slot. Then shut the machine down, and restart it, holding down the D key on the keyboard. (You may need a wired mouse instead of a wireless mouse.) Click thebutton to run the tests. If it says you have a problem, WRITE DOWN exactly what the diagnostic message was.
The Apple diagnostic runs a simple memory test. If you suspect that you have a memory problem, you may want to download and run memtest. There is also a (free) point-and-click interface to memtest called Rember that you can download.
If you've had disk problems or system crashes, the contents of your file system may be corrupted. Once that happens, your computer will run even worse. Boot the computer from the install disc while holding down the C key, and instead of installing the operating system, choose. Then highlight your boot drive in the left sidebar and click . If this process finds and fixes problems, then something bad happened in the past: your hard drive may be getting ready to fail, so do a backup. Running Repair is always OK to do: it never makes things worse. Sometimes Disk Utility will say it cannot fix your disk; this is big trouble, and you may end up having to wipe your disk, reformat it, and reload from your backup.
Every file on the computer has permission settings that say whether the file can be read or written. These permissions sometimes get set wrong, for instance if you have trouble installing or removing an application. A few applications' installers don't set permissions the way Apple thinks they should be. You can run Disk Utility (no need to boot from CD), select your boot drive in the left sidebar, and click. This will take a while and may produce a list of messages saying it changed something. It's always safe to do this repair, and doing it may help sometimes.
Before a problem started, did you "clean up a lot of stuff you didn't think you needed?" This is a common cause of difficulties. You should be running Time Machine. If so, you may be able to restore the deleted files.
Boot the computer from the install disc while holding down the C key. The Installer window will come up. Tell it to go ahead, and wait while it reinstalls the OS. Takes an hour or so. Then go intoand re-apply all the software updates. This process won't delete your personal files or data.
For some WiFi problems, you may need to open your system keychain and delete entries for "Airport" and re-create them.
If your computer won't eject a CD with ⏏, try
If your computer displays and alert box about "failed to calibrate the laser power level" when trying to write a CD or DVD, use the Laser Lens Cleaner and try again. If you insert a CD that has read errors, it may take several minutes of grunching and retrying before the OS gives up on it and ejects it. Run the Lens Cleaner before trying it again.
Networking problems are hard to diagnose. If you have trouble with wireless networking, try
A manual came with your computer. Read it.
Try searching Apple's support site for help. In the left hand panel, pick your product from the "all products..." selector, and then look under "Troubleshooting" on the resulting page.
You can also search for help on Google.. but beware, sometimes you find wrong answers there. Same is true of the Apple Support Discussions pages.
When you run out of things to try, call AppleCare. You bought AppleCare with your computer, as I suggested, right? It is essential. (It is not available in all countries though.)
Before you call, find your computer's serial number and make some notes about what your problem is, and what you have tried (see "Reporting a Problem" above). I used to put a sticker on the front of each Mac with its serial number and the phone number of AppleCare. I think Macs are more reliable now: I have called AppleCare about four times in the last ten years.
The time may come when your computer does not work, and the AppleCare specialist says "bring it in to service." If at all possible, take it to a real Apple Store rather than to an "authorized service provider." I had really bad experiences with the supposedly expert service people at CompUSA. Not all non-Apple repair places are bad, but the good ones are hard to find. For some kinds of problems, Apple may arrange for shipping.
So, you took your machine in to the Apple Store, and they worked on it and gave it back to you. What next?
Your hard drive may have crashed. Apple repair will have installed a new hard drive, and usually re-installed the OS. So this is like having a new machine. The machine will go through the "first boot" sequence when you start it up, and you will have to restore your files from your Time Machine backup, or other backups. If you don't have a backup, you are in big trouble. You can ask Apple to give you the old crashed hard drive, and then you can Google "Drive Savers," and perhaps pay thousands of dollars to see if they can recover your data.
In some cases, the "mother board" or "main logic board" has to be replaced to make your computer work again. Your files may be all just fine.. but things are not necessarily perfect. There are two possible pitfalls.
One thing that can go wrong is that the Apple Store techs may have forgotten to transfer your old serial number to the new machine. If this happens, and you have any applications installed that are locked to the CPU serial number, they won't run. Adobe Photoshop and Illustrator behave this way. If this problem occurs, you will have to call Adobe Tech Support for help. (They don't work on weekends.)
Even if the serial number is correctly transferred, you will discover that the machine has a new MAC Address. (What's that? It's a number that identifies your network adapter, and no two machines have the same one.) This matters because Time Machine uses it to identify backups: so if your MAC address changes, then Time Machine won't see your old backups, and you may have to do some adjustment to get it to start backing your machine up again. The solution to this problem is different for different versions of OS X; search Google for advice if you are in this situation.