ASUS P5Q cpu overheat

Hello everyone,

I'm having a problem with my CPU and Mobo.
I set up a Asus P5Q mobo with a Intel Core 2 Quad 2.83 MHz cpu.

The computer has running fine for the last few days, and even this morning, but since I've gotten home from work, the cpu is showing temps of 100 degrees Celsius and above.

I updated the bios on my mobo, and now it shows closer to 80 degrees Celsius, but the computer shut itself off moments later.

Just for clarity, when I used it before I kept an eye on the temperatures, and it would peak at 45 degrees.
Any ideas?