i know this is an old thread, but im new here and this is already the second time ive seen talk of the 8500's CUDA button and removal of the motherboard (which is a rite pain)

On my 8500 there is a plastic hinged arm holding the daughter-board down into the socket, its lightly latched to the base of the power supply frame thing, all you have to do is unlatch it, flip it back, remove the cpu and use the backside of an inkpen to press the button