Heatsink Fan Not Spinning

My heatsink fan spins normally when I first start the computer up, but slows down and stops when the computer is starting up, only to start spinning again when Windows is fully loaded. I have an Athalon 64 3400 with the stock heatsink. Thanks for your help.

That is strange. It almost sounds like something is draining power from your fan in the hardware.

I'd try replacing the fan and see if it still happens. If the problem is fixed, then you know it was just your fan. If the problem persists, then I'd question your motherboard. A motherboard problem would be less likely.