Please explain what actually happens? I see reference to locking up, and then a reference to shutting down. What is the actual, observable behavior? I'm slightly confused, so it might make sense to see if the OP can provide more detail into the "what happens" section of information gathering. If it locks up with no BSOD, we might want to try crashing the machine via a PS/2 keyboard to see if the hardware itself is hung, or just the driver framework.
