I just wanted to add that what was happening to your girlfriend sounds like a driver reset (often referred to as a TDR), probably related to stress since underclocking solved the issue. I've had this happen to me in this game and numerous games; however, this one handles them a bit less elegantly. In other games, the screen just freezes up as sounds resume. Then I see a Windows notification at the bottom right that says that the graphics driver has successfully recovered. Then the game either proceeds as normal or becomes super laggy until restart. This game, however, causes my monitor to lose signal when this happens. Once my graphics drivers have reset, I simply see a DirectX error generated by the game. But if I go to Event Viewer, I see an event corresponding to the TDR.

I experience them very rarely now, but it used to be extremely frequent. This is specific to my card, but the fans won't spin faster than 30% without software intervention, so my card was constantly overheating. I run Precision X with an aggressive fan curve to help keep it cool. I would recommend restoring the factory overclock, forcing the fans to spin at full speed for testing, and checking them for dust. It may be something else, but since the last patch, my card has been running *way* hotter for some reason. In fact, I've experienced 2 TDRs thus far, whereas before, it was never an issue with this game. But I can confirm that heat is the problem in my case (but I *am* on an old potato!)