OS restarts on Boot

Last night, I plugged in another HD to back up something. The strange thing was, I had to boot in safe mode, or else windows would not get past the splash screen.

today, I replaced it w/ the 2nd HD i normally have in my computer, and now when i boot the splash screen appears, adn after a minute the computer reboots. If i boot in safe mode or last good config, it reboots after about 2 seconds. When I boot from the XP disk, it doesnt recognize the XP installation, or the type of partition. CHKDSK says "one or more unrecoverable errors", but it shows that instantly, like it isnt even checking the HD. When I boot using Partion Magic, it sees the NTFS partition w/ the system on it, and then it sees a HTFS partition that is full (I had a 2nd NTFS partion on that drive). Deleting the HTFS partion gives an error.

I dont think my HD is bad, because i run disk check weekly, and have had no problems until today.

Any ideas?

anyone?

I'm not sure if I should replace the HD, or just reformat. I dont want to reinstall eveverything just to find out the HDs bad anyway.

If chkdsk won't even run, there is a good chance the hard drive is dead. I'd re-partition and reformat, then try to run chkdsk again and if it still doesn't work, replace the drive.

Yea i would try formating and then see what happens.

alright well after spending days attempting to back up data, as soon as i got everything backed up, my computer just magically started working. No errors on the HD.

I think I have some clue what might have happened, but its too strange to explain. I think its related to problems with some guys computer I was helping to fix.