I was going to say that you are overheating, but I don't think that would cause freezing/crashing, but definitely a restart. Check temps anyway. Try to find a patch for the game, and update all your drivers. Does this happen with other games? Is it when you are at a certain spot in the game, or just after time? Does it happen when you see a certain object in the game? Read the buglist, make sure your card is compatible with it. Maybe try to turn the graphics down.