MacBook has fatal error on startup

Question

Hi,
My macbook has just this morning - when I needed to email an assignment to a professor of course - has started to experience fatal errors on startup. The computer starts up normally,and once the desktop has loaded, a dialog comes up saying something along the lines of "Mac OS X has experienced a fatal error and must restart in 3 seconds." I brought it quickly to an authorized apple service store, but they couldn't do anything for the problem except start a program right when the dialog came up to block the shutdown process. However, I had to go to school, so while I was in class I downloaded TechTool Deluxe and I've been running it. It hasn't found any errors, so I don't know what to think about the startup problem. I was wondering if anyone had any experience with fatal errors on startup?
Also, the technician who helped me this morning said that it could be either a problem with hardware or software, but that if it was a problem with software, the diagnostic would not be covered by AppleCare. Since I'm trying to save as much money as possible as a student, does anyone have any tips as to determining whether this is a software issue, so I don't have to pay for a diagnostic check-up?
Thanks in advance!

Answer 1

Boot from your OS X Installer Disc One that came with the computer. After the chime press and hold down the "D" key until the diagnostic screen appears. Run the extended diagnostics multiple times over at least several hours. If any errors are reported note down the error code(s) and report them back here.
If you get an error code with MEM in it that means bad RAM. HDD refers to the hard drive. MOB is the motherboard.
If you don't get any errors then try reinstalling OS X:
How to Perform an Archive and Install
An Archive and Install will NOT erase your hard drive, but you must have sufficient free space for a second OS X installation which could be from 3-9 GBs depending upon the version of OS X and selected installation options. The free space requirement is over and above normal free space requirements which should be at least 6-10 GBs. Read all the linked references carefully before proceeding.
1. Be sure to use Disk Utility first to repair the disk before performing the Archive and Install.
Repairing the Hard Drive and Permissions
Boot from your OS X Installer disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Installer menu (Utilities menu for Tiger.) After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported, then quit DU and return to the installer.
2. Do not proceed with an Archive and Install if DU reports errors it cannot fix. In that case use Disk Warrior and/or TechTool Pro to repair the hard drive. If neither can repair the drive, then you will have to erase the drive and reinstall from scratch.
3. Boot from your OS X Installer disc. After the installer loads select your language and click on the Continue button. When you reach the screen to select a destination drive click once on the destination drive then click on the Option button. Select the Archive and Install option. You have an option to preserve users and network preferences. Only select this option if you are sure you have no corrupted files in your user accounts. Otherwise leave this option unchecked. Click on the OK button and continue with the OS X Installation.
4. Upon completion of the Archive and Install you will have a Previous System Folder in the root directory. You should retain the PSF until you are sure you do not need to manually transfer any items from the PSF to your newly installed system.
5. After moving any items you want to keep from the PSF you should delete it. You can back it up if you prefer, but you must delete it from the hard drive.
6. You can now download a Combo Updater directly from Apple's download site to update your new system to the desired version as well as install any security or other updates. You can also do this using Software Update.