I've sold a couple of PCs recently that had no issues in any benchmark/stress test I put them through, but as soon as the customer fired up a game, problems occurred. With one, it was WoW and at random times in the game - sometimes minutes, sometimes hours. In another, it was whenever it would pop-up an overlay screen for inventory management (I forget the game) - as soon as he exited to get back to the game, it would crash. In both cases, it was a faulty memory stick. We found it by removing a stick at a time until the game ran. Replacing the bad stick fixed the issue. It's rebooting, probably, because you're getting a BlueScreen and the PC's rebooting immediately as it dumps. If you have two sticks of memory (or more) try removing one at a time to see if you still have the issue. If you have just a single stick, try running MemTest86. It's not always accurate, though, because it didn't find any errors on either of the two PCs I had issues with. Go figure. Usually, though, when I see game crashes involving reboots and not simply kicking you back to the desktop (which would be a game issue or a driver problem) it involves a bad memory stick.