This happened to me a while back.
Did you vac the cooling ribs through the fan on the board, as a lot of dirt can build in them making the pc run hot. I downloaded a free program called "speedfan 4.38", it gives info on all temp's on your pc. I made a device from a arosol lid a 12in long thin tube (to fit through the fan blades) and some tape to pop on a hover pipe and hover all the hard to reach gaps.(DONT HAVE IT ON THE HOVER TOO LONG IT WILL OVER HEAT)
my fix was to take out the power pack from the tower, unscrew the cover & vac the inside, mine was thick with crap/dirt.
lots of other info on this site its helped me with heat problems on other pc's in the past. Hope you fix your problem.
http://www.computerhope.com/issues/ch000689.htm
Erk, July 2009
