Have you shorted the jumper? It should be a three pin with a small piece of plastic (with metal in the middle), covering two of the three pins. It should be located somewhere near the cpu socket, you'll just have to look for it. To short the jumper, take the piece off and move it to the opposite two pins. Return it to the original position, and give it a go. I would do this with the battery out, and the PC unplugged from the wall.