I am running an ASUS A8NSLI Motherboard with an ASUS Extreme N6600GT graphics card. The system shuts down with no blue screen and won't restart. At times, it doesn't reach the BIOS screen.

I recently replaced the heatsink. All cases fans are working. I think the graphics card fan is making a high pitched sound before shutdown. It's extremely hot here, and the CPU typically runs at 35 - 40 degrees.

Even now, I am getting no indication that the CPU is hotter than 40. (when the computer is running stably).

Whatever advice you could give about what could be causing this problem would be greatly appreciated.