This is happening to me now.. Tried everything listed in this thread: Reinstalled, verified, putting it on lowest graphics, windowed mode. It only happens on NW, I have been playing Fallout, ETW, and loads of other games without any problem.
If anyone knows a solution, I would be very gratefull.
EDIT: Nvm guys, just removed some dust from my ventilators. It was overheating! D: