I agree, it sounds like Hard drive failure. Before you do anything drastic you might try booting into safe mode. Tap the F8 key continously while computer is booting if the HD is not completely shot, you will see the safe mode open. If it does, use the arrow keys to move up to the "last Known Good Configuration" choice and click enter. Let the computer do it's thing,. If this works, click on computer (in XP my computer), right click on your c drive, select properties, click tools tab.click on error checking. Check both boxes that come up to scan;/repair the disk. It will tell you that it will run when you reboot the computer. Select Okay, reboot the computer.
This error checking can take some time to go thru the steps,
Good Luck
Vicks