[Saber Cherry]

I'm going to guess that your motherboard was made in Taiwan with defective capacitors. Look at the board and see if any are bulging or leaking. They should be perfect cylinders. Of course, even if it looks fine, I'm still going to guess that's the problem.

If there is a heat problem, you can probably solve it by underclocking the CPU or video card, which is a lot easier than messing around with stuff inside the case.