In reference to what Cbakey just posted about the Asus a7n8x Dlx mobo, I had one of those up until just recently. That was the only board from Asus I had a minor problem with.

My problem was that the mobo cpu diode temperature sensors were reporting an abnormally high temperature. It's a common problem with that particular board, I found. the reason this can be a problem is the built-in protection the latest Asus boards have. when the cpu temp reaches a certain point the system automatically shuts off. In my case it was shutting off when the actual temp was only at about 45 degrees. I replaced it with the Asus A7N8X-E Deluxe and the bios reports the actual temperature.

Cliff notes:
Asus A7N8X Dlx has a common problem
Asus A7N8X-E Dlx does not have that problem.