Please read your post and see what you left out. All I can do is note common reasons such as too small power supplies that are a common source of error as well as drivers. Microsoft does not install drivers for us.
Tell more about the machine, the game, the power supply and if the case cover is off and the fan pointed at the machine.
My friend's computer keeps restarting whenever he plays a 3D game. We have tried many things. we do not beleive his video card is overheating because he has a fan blowing straight onto it. He has checked for viruses... he has checked his capacitors... he updated his windows, (windows ME)... and he has done everything everyone has said it might be. DOES ANYONE KNOW WHAT MIGHT BE GOING ON!!!!!!! thank you in advance.