Sounds like a power problem of some sort. Could be faulty power coming from the wall socket, the power supply giving faulty power to the motherboard, or something on the motherboard failing.
Assuming your wall voltage is OK, I would suspect the power supply first. 500w watts is plenty, but even though it is 80 Plus Bronze Certified, Coolermaster power supplies are not very good. I think either they paid for their certification, or someone at 80 Plus was asleep that day.
I have the 450w version, and it had trouble running a 300 watt system. I moved it to my HTPC which is just a basic system with integrated graphics(about 125w under load), and it does fine.
Next I would suspect the Power Color video card. They are also not of very good quality. If it is trying to draw more power than the motherboard slot can supply, then that could cause a surge issue, although really, your machine should really shut down at that point, not reboot.
The only real way to troubleshoot this is to swap out components, or even better, try them in another system one at a time.