My CPU fan was stopping on occasion, a little clean air and it would run. After a while I figured I'd better just buy a new one. After only a couple of weeks this one does the same thing. The computer runs just fine otherwise, with the excetion of it sometimes not wanting to come out of sleep mode,
Check to see if there's a BIOs upgrade for your motherboard. I had a problem with one of my board where the CPU fan wouldn't start back up after coming out of suspend or hibernation. The company that made my board came out with a BIOs update later that fixed the problem.