My Mac is completely dead, it just won’t boot up - what’s wrong with it?

This can be caused by a number of problems. Listed from most likely to least likely:
1. The operating system is damaged or corrupt, most likely due to a hard disk directory error. A program like DiskWarrior can fix this.
2. A device connected to the system is malfunctioning or defective. i have seen this "gray screen" hang on modern Macs caused by a defective mouse, and also by a defective external USB CD recorder. Have them disconnect everything, mouse, keyboard, etc. and try turning the machine on.
3. A defective or failed hard drive. If the computer can boot from a CD, but running Disk Utility shows no hard drives connected to the system the hard drive has failed. Some hard drive failures can also prevent booting from a CD-ROM on the same IDE chain; the hard drive's ribbon cable must be disconnected to test this.
4. Bad RAM. This will cause a gray or black screen, and in some circumstances, it just hangs, and is often accompanied by a long tone on bootup.
5. A bad power supply. Often indicated by a sysem that powers up and then either powers down right away, or makes a "clicking" sound followed by a power down.
6. A bad logic board. If you can boot up into firmware prompt window, then you know that the logic board is OK, otherwise you won’t get anything if the motherboard or the power supply is faulty. Time to visit your local Mac repair center.

What can I do about continued freezes and crashes?

There are a number of things you can do to reduce or even stop the crashes you’re having, these are often to do with the hard disk or possible hardware faults, normally RAM modules. Go through this checklist to remove any of the usual culprits, and then you might narrow it down to hardware or a specific piece of software you recently installed:
1) Hard disk corruption. Do a repair on the main system disk first and then with all other partitions and/or external hard disks.
2) Bad RAM modules, can certainly cause hard system wide crashes, and can go faulty even when you’ve been using them for a quite a long time. Best thing to do is to remove all recent RAM, and leave 128mb in the Mac, so that you can test it. If it boots up OK, and all programs function properly, then one of the modules you removed is bad, all you can do is fit them back in one at a time until things go wrong again, then you’ll know which one is bad.
If you want to avoid taking out RAM, then you can use a program to test the RAM for you. TechTool Pro v4 has an extensive array of tests it can perform on RAM, so if you have that program, use it.
3) You’re low on RAM. In order for MacOS X to operate within a comfortable amount of memory, you need at LEAST 128mb of RAM, although 256mb or more is recommended. Since RAM is quite cheap these days, buy as much as you can afford, and as much as the Mac will hold, meaning, the number of RAM slots will govern the amount it can use.
4) Preference files can sometimes get corrupted - bin the one that belongs to any programs that crash often. You will find them in your User folder, in the Library/Perferences/ folders.
5) USB or Firewire peripherals can cause ‘hanging’, while the system tries to communicate with it. Best to disconnect them, and then start using your Mac as normal, and see if the problem goes away.
6) Repair the permissions on the main system boot disk. Use Disk Utility to repair them - doing this will reset all system file permissions to their default/correct state, allowing the OS to run properly without unexpected quits when accessing files.
Sometimes it is necessary to repair permissions after doing a MacOS X update, but only if things start to go wrong after the update. If your system is stable, then you do not need to do it.
7) Lack of disk space can be a major factor with OS X, as the OS needs extra disk space to save it’s swap file (virtual memory). You need to allow for at least 500Mb of disk space for virtual memory to do it’s thing, otherwise you’ll get regular crashes until you can free up some more space on the System partition/disk.

This program(s) keeps 'Unexpectedly Quitting', what's going on?

The one thing I find that is nearly always responsible for this particular problem, is when the program’s preference file has corrupted. All you have to do is to go into your User folder, and find the folder called Library, in here is the Preferences folder for all the programs you’ve used. However, since Apple has decided on changing the naming conventions for pref files, it makes finding it a little confusing. Look for either the URL of the company that made the program, or the programs’ own name, and bin the pref file. Then see if the program will launch again. If the program won’t load up, you may have to reinstall it.

Permissions can also compromise applications if the system default permissions are not correctly set. Run Disk Utility (OS 10.2/10.3) and click on repair permissions button to initiate the repair on your hard disk.

Another reason why some programs may be quitting, is that for some reason, parts of the program's extraneous files are corrupted or deleted. You will have to reinstall the program from the installation disk(s), to correct this problem.

It is also a good idea to run a disk repair application over your main system boot partition or hard disk, as disk errors can cause all sorts of havoc with your system.

Lastly, if all the above fails to resolve the problem, then you'll have to do a clean install of MacOS X from CD/DVD.

I just installed OS X 10.2x, and also the screen remains dark throughout bootup and in the Finder, what do I do to get it back to normal?

This is likely to happen when you’ve install OS X on an old G3/G4 Mac, and will probably happen on a Mac with a built-in screen. This usually means that you haven’t installed the firmware update, so that the Mac is optimised for OS X.

To get the monitor/LCD to work as normal, you will have to boot into MacOS 9.1 or later (depending on the firmware update’s requirements), and send it to sleep by holding down the power button on the keyboard for a couple of seconds, and release it, then press the ‘s’ key to send it immediately to sleep. Wait several seconds, and wake it up again - do this only if the problem persists in OS 9 as well. Then apply the firmware update as per the instructions. Now boot into OS X, and everything should be OK.

If that doesn’t work, then reboot the Mac and zap the PRAM (see Keyboard Shortcuts section). This will remove the monitor resolution settings from memory. Now bootup into OS 9 or system CD and see if this cures the problem. If it does, boot from the hard disk again.

How do I use ‘fsck’ from the Command Line?

First, what is ‘fsck’? It is a disk repair command that you can use from the Terminal interface.

Once you have reached the command line, follow these steps to use fsck:
1. At the prompt, type: fsck -y
2. Press Return.
The fsck utility will go through five phases, and then return information about the disk's utilisation and fragmentation. If fsck alters, repairs, or fixes anything, it will display the message: ***** FILE SYSTEM WAS MODIFIED *****
Important: If this message appears, repeat the fsck -y command until this message no longer appears. It is normal for your computer to require several passes of fsck, because first-pass repairs may uncover additional errors.
3. When fsck reports that no problems were found, type: reboot
4. Press Return.