I don't normally deal with Windows but someone wanted me to fix their computer with Windows XP on it. It was just restarting every time it tried to boot. It would not go into safe mode, the result was the same regardless of the selected mode.

The computer is like 4 years old and has been running the same installation for that entire time, so I figured the easiest solution was just to back up their files and re-install. I loaded the computer up with a live CD and copied their files off to a USB drive, then proceeded to run HP's "factory restore" feature (which I'm not particularly fond of, I'd rather have a disk to install from than reload all the crapware HP gets paid to install for you). It restored, and I put all their files back, installed their programs, and started the full windows update process. Everything seemed great so I left and told them what to do once it finished.

A few hours pass, and my phone rings. Apparently it started doing the exact same thing as before once the updates finished.

I don't have the computer sitting in front of me now so I can't really provide any more information than that.

What could be causing this and, more importantly, how do I fix it? The fact that the same problem resurfaced after the restore makes me think it's either a hardware problem or an update breaking the computer.