Sounds like overheating issue. Make sure your computer is receiving good airflow and the air that is coming in is not too hot (i.e. run an air conditioner in your computer room).
Thanks for your answer but this happens only with the game. I left turn on the computer all day and it worked well without interruption. Not only I reduced the resolution 800x600 and for now works. The case is a Lian-Li and it has good airflow. Out of curiosity: is there a tool that display the cpu temperature ? Regards Alessandro