its either the fan itself. or the power terminals. before u go out and buy a new fan, i would first recommend getting a volt meter and checking to see if u have voltage at the terminals where the fan is hooked up. if u do have voltage, then its a bad fan, if u dont, then its a bad connection between the motherboard and the power jack u plugged into. i had the same problem with my old computer, except the fan was in the power supply. turns out the fan was still good, it was just a bad electrical connection between the fan and the circuit board.