What kind of cooler do you have? And you may need to remove it, clean the gunk off, add fresh goo and re-seat the cooler. Gunk have a tendency to "dry out" and lose efficiency with time.
Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn!
"The sky was the color of a TV tuned to a dead station" - Neuromancer