Random Computer Shutdown Issue

So once I installed W7 beta I was just going around and installing all the programs I needed, when a strange error occurred while I was trying to install AVG, this error didn't give me a message, a warning or anything, but in the middle of the installation my computer just shut off.

While confused as to why I was looking at a blank screen all of a sudden, I restarted my computer, windows 7 booted, I sent an error report, and everything seemed to be working fine, until five minutes later when it happened again, and this happened to me every few minutes of use.

So I got fed up and decided to just go back into my xp partition, but while xp was loading, it happened again. So I could no longer access my xp partition because my computer just spontaneously shuts off every time. I restored until a time before I got the error and everything seemed fine again for some time, W7 wouldn't shut of randomly and I could go into xp.

So about 20 minutes later, while I was installing TF2, it happened again, and I couldn't get into xp again. So I did what I did before and recovered, but this time, I can go into W7 without random shut down, but not into my my xp partition. This is a real big pain in the ass and I would apprieciate any ideas on how to fix this. I'm about to just reintstall windows 7 and see what happens.