3D games are video and CPU intensive, check your BIOS cpu temperature threshold, 60-65C shutoff would be too low. Get furmark or other video card stress test software and see if your video card is not overheating in the modes you use for the game. Finally, put the game in lowest video mode (res. 720p) and no filtering or anti-aliasing, see if the system can handle it then. Turn video card fan on 100% from boot time.