Computer Powers Off after turning it on

[thejerkface]

My PC keeps turning off after turning it on. It'll go through the boot process and load XP, then after 5 mins or less, it'll turn off. My PC is custom built and about a year old. I scan for viruses regularly. However, I can't really check for new viruses again b/c the computer doesn't stay on long enough. I think it might be the power source that is causing it. Any ideas on what it could be?

I just bought a new laptop and I really just want to get my files from the old desktop onto it. I have other PCs around the house. Can I remove the hard drive from the malfunctioning PC and swap it into a working PC in order to access my files (assuming it's a power problem and not a virus)?