Computer Restarts Without Warning

I have a computer partitioned into two parts, both running Windows XP SP2. The smaller partition restarts whenever I perform a routine such as starting device manager from the help screen. Unfortunately, I am not able to log onto the internet using this partition due to a seperate (unrelated?) problem.

Can any tech savvy persons help me troubleshoot this problem?

Thanks in Advance.

 

Update- Problem Solved!

The problem was with my mmodem drivers. On the direction of my ISP I uninstalled my modem, then attemted to reinstall it. The computer crashed a few times, giving me several BSODS. But I rebooted into safe mode at which time the computer recognized the modem and reinstalled the drivers.

After this I ran several routines from the Read Me First thread in the Malware section of this bulletin board. Especially CCleaner, which I ran from all desktops and in Safe mode.

The computer runs fine, now.