Standard ATX motherboards feature a single 10x2, 20 pin connector for the power supply. The connection features a sort of a simple latch which is released from the nub on the motherboard connector by depressing the top of the latch (just below my thumb). You can also see the nub on the motherboard connector, on the side near the motherboard edge. It can take a bit of force to pull the connection out of the motherboard even once it's release, since there are 20 tight connection, so be prepared to use your off hand to hold the motherboard down if the edge lifts as you remove the connector.
