Wow. Hard shut offs? Yeah, my first thought is heat too.
Download Nvidia's Ntune product at
http://www.nvidia.com/object/ntune_5.05.54.00.html . Run "Nvidia Monitor" and when it opens, click the little arrow in the bottom right to see a graph of the temperature of your video card. It will also tell you how fast your fans are spinning, etc.
His computer might also be suffering from lack of power. Hard shut offs will kill you if the computer tries to draw more power than the supply can handle. I would make sure the components on your machine aren't too much for the psupply you put in there.
--Locane