Might sound dumb, but do you play any other games? I've had this happen playing 1 game, but not another. It's really finky. If don't, but have some? I'd start those up, especially one that is resource intensive. If it happens on that, you've probably got a bad power supply.

This happens to me a lot. Only game that does this. No warning just black screens and reboots after two to maybe 15 minutes of time then shutdown. So putting it on the shelf until next patch.