@vonny,
Speaking of which, have you had the problem since you adjusted the surface it was on?
Rockhead, if it isn't already, you might try removing the cover to the CPU box to allow it more air circulation. While it is open, blow out any accumulating dust, dust bunnies and anything else that could be blocking vents and air flow. Also, if you have an extra room fan, aim it at the CPU box when it gets hot.
My computer gets finicky when it gets too hot for the swamp cooler to keep the room below 90. When that happens, I just remove the CPU cover and it seems to solve the problem.