Vista help

Hello,

I have an issue with my computer shutting down after 10 minutes of operation I have changed the power supply and the motherboard and the same problem occurs. I have read on here about the CPU overheating, but the fan is running on the cpu the whole time and I also have two auxillary fans for the case and have been running the computer with the side off so that there is more airflow. How do I know if this is my problem or could it be my hard drive malfunctioning? I don't think it is a hard drive malfunction, but maybe a virus, but how to fix it when the computer wont run long enough to run a scan? Any help would be appreciated. Thanks here is the setup that I have running.

XFX nforce 780i SLI motherboard
Intel dual core processor
2GB RAM
Geforce 8600 GT video card