This thread has partially answered my question. I have the same problem. When I connect the iPac with a PS/2-to-USB convertor, the switch turns on for a second, then turns off. But if I connect the iPac directly to the mouse or keyboard PS/2 port on the motherboard, the controls are completely unresponsive. I don't know what else to do. I have the iPac 2 if that makes any difference.