well Flashy... chav and entwisi told you what you should do:
go into bios settings and look under where it says cpu temp
leave it running for a few mins and keep an eye on teh temperature while you are still in the bios screen ( do not boot windows)
if your starting to hit near 40%c and above then its most likely your cpu/processor not been cooled down enough and a simple cpu fan exchange may be all u need
40 degrees C is cool even for an athlon, modern CPUs run up to 85 degrees
it could be a crack on teh motherboard, have you fitted anything new recently? Memory/gfx card etc?
simple eh!
