Computer shut down and I lost files...HELP!

Question

I was using my Powerbook on battery power and it said that I had about 20 minutes remaining. Suddenly my computer shut-off.
I connected the computer to the power source and when I started it back up my desktop was changed back to the default, the files were gone from my desktop, and everything was restored back to default settings. I lost all of my files.
The strange thing is that I had fast-user switching turned on with a guest log-in and that account was completely fine.
Any help would be greatly appreciated. I have a project due on Monday and I need my files back. Thank you.
-J

Answer 1

OK, my 'Hitchhiker Guide to the Galaxy' says "DON'T PANIC" on its first page. If you're near an Apple Store, take it to an Apple 'genius'; if you're at a university, take it to a very highly respected Unix administrator. Never take it a friend.
Your computer should run fine with the battery removed, using just the wall cord. Your guest account is fine because that is just a sequence of directories & files on your hard disk, placed elsewhere on the disk. It may be that a file or directory necessary to login to your account (a corrupted file in the desktop subdirectory, for example) has caused your Mac to abandon the boot, booting instead in 'safe mode', creating a new account (new files) placed on the disk after your guest's files. Remember, I'm only guessing. This would mean all your files are fine, but someone needs to either repair your disk, or move all the files they can to a new directory structure. To be safe, don't write to your disk.
If you have a hardware test CD and first Mac OS X DVD, you could 'repair your disk' and its 'permissions'; but I advise against this until the problem is correctly diagnosed. You don't want to lose your files. Instead of the above, if a friend's Mac and Firewire cable are available, you could boot as an administrator (modify Guest using your login password, for example) and click 'System Preferences > Startup Disk > Target Disk Mode > Restart'. If you connect the Firewire cable to your friend's computer, he or she will have access to all your files: possibly the ones you want. This is a benign procedure, not writing to your disk.
Copy these files from 'My Hard Disk > Users > My Name > Desktop' to your friend's computer, or anywhere you can finish your project. Copy all your Preferences, Keychain, &c (if you can) before taking your computer in for repair.
My next rule: the most fragile file on your computer is your 'Desktop'. Never, never, never save a file on it. MicroSoft, in its wisdom, overwrote any files stored on it when booting in 'safe' mode. (Note the quotes.) Surely Macs are more intelligent, and have a genuinely 'safe' mode. The rule: only aliases of files or folders should ever appear on a 'desktop'. Their loss is inconsequential.
Best of luck. Remember, some 'repairs' of defective disk blocks involve marking them unavailable, meaning your Desktop is unavailable to Apple's tools; or repairs involve local reformats (copying a good block over it), creating the same problem, or worse. That's why you need a seasoned Unix professional with fancy tools. (Ask around Math & Physics Departments; a good administrator is an old guy who speaks English, not a 'geek', and will be happy to help.) I wouldn't take a chance with anyone else.
Bruce Bathurst, PhD
Retired Supercomputer Consultant