If you unbolted the head and laid it down, you likely disconnected one or two connectors in the head. Bottom left connector on the CPU is especially short, and goes to the coin door. Once the wires and connector get loose, they can fall through the big hole in the bottom of the head into the lower cabinet, so it looks like nothing is loose when you open the head. With the power off, fish around in that hole to look for loose connectors. I'll bet you'll find one or two loose there. Match them up with the right connector in the head and you should be good to go.