can't even log into the desktop

Hi konrinn, and a warm welcome to the forums! 🙂

Could be many things, we should start with this since it is Disk Problems likely...

"Try Disk Utility

1. Insert the Mac OS X Tiger Install disc that came with your computer, then restart the computer while holding the C key.
2. When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu. (In Mac OS X 10.4 or later, you must select your language first.)
*Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.*
3. Click the First Aid tab.
4. Select your Mac OS X volume.
5. Click Repair. Disk Utility checks and repairs the disk."

http://docs.info.apple.com/article.html?artnum=106214

Then try a Safe Boot, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, reboot when it completes.

(Safe boot may stay on the gray radian for a long time, let it go, it's trying to repair the Hard Drive.)

Very Important, how much Free Space is on your Hard Drive first of all?

will the original files and date in the disk be gone?

Hopefully not, in fact it should prevent further loss, but it's always possible that with a Hardware problem like RAM or HD going out that it could get worse, most often it'll be better though.

Have you tried just this part...

Then try a Safe Boot, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, reboot when it completes.