I have not been able to determine a pattern for why this happens, despite my best efforts. I've attempted to run it on full power with Prime95 and this doesn't trigger a restart. Generally the restarts occur while I'm playing games, watching videos, or even just having multiple tabs open in a browser. However, I often play processor intense games for hours without any restarts occurring, and sometimes they'll happen 3-4 times in an hour during less intense activity, so I don't think that is the problem.
I imagine it has something to do with overheating or power consumption so I've been monitoring CPU temperature and cleaning with compressed air, but the problem keeps happening. I don't know how to track power consumption, and assume that this is the problem. Whenever this occurs, the sound gets stuck in a short loop of whatever was playing at the time, though restarts also occur when nothing is playing.
Here is a screenshot of temperatures:
and under load:
Here's the parts list: http://secure.newegg.com/WishList/PublicWishDetail.aspx?WishListNumber=10546754
As shown in the list, the case includes a 585W Power Supply, which I've been told should be plenty.
I built the computer myself with a friend's guidance but it's very possible I did something wrong. Right now I'm looking into ensuring that I have the latest drivers for all components. Any help would be appreciated- thanks.