Freeze up problem

[btb103]

I just built a computer for a friend and after like a week of running the computer is freezing up every ten seconds or so. In windows task manager I see that the System Idle Process is running with above 95 CPU usage and presumably is spiking at 100 when the computer freezes. As per the suggestion of another friend I made sure that the system wasn't running too hot (44 proc, 29 case), switched the RAM, and played with the virtual memory settings. I don't know what else to do, I guess next step would be to reinstall Windows but I would like to know if there is an easier fix.

Specs are as follows:
Gigabyte GA-7VM400M-RZ (using onboard video and sound)
AMD Sempron 2500+
pqi Turbo 512MB PC3200

Thanks for your help!