computer shutting down

Working on a GA 7n-400 mobo with a 2800 barton running xp home and it recently started shutting down by itself (no power to mobo).I thought it was the power supply but now believe I have narrowed it down to cpu heat and was wondering if this combo has a shutdown feature which I can not find in the bios?Bios temp says 98 F and sandra says the same.Box passes all sandra test but when I try the cpu tests it last about 2 seconds and shuts down dead and the hs is almost hot to the touch.I will try resetting the h/f.

Btw pc is running all stock settings along with the ati9200 vid card.

Never mind I took the hs/fan off and yuk!The cpu melted thru the tape down to the round copper insert thats in the aluminum hs.Tape melted around the cpu edges - surprised it even works still.