First thing you can do is open computer case and clean, with either an air can or something else that blows air with force or at last resort a vacuum cleaner, the heatsing and CPU fan and while you are at it all the dust and debris inside the case.
After you have done so turn on PC and see if all fans are spinning properly in case of an error.
I'd vote for Dust on fan and heatsink, I've seen a lot of similar problems in the past and the worst has been an inch thick.............feels like wool when u touch it..........