[IceCube!]

I doubt its over heating as MOST computers beep once if they over heat when they shut down, which he hasnt said in his post. Do you get a blue screen? Does it just shut off? Or somthing elsE?

EDIT: Also if you have a custom Processor you will get a warning appear in the corner of your screen which can be adjusted in the CPU config. Which will close programs that use the CPU to prevent it from shutting down, or atleast mine does