There is a second 4-pin that plugs in a different place than the 20-pin. Thought that might be it because I got similar simptoms with my first build. I didn't plug the smaller pin in. Was thinking that the one longer was all that was required. Looking at your board I see an 8-pin that is at the top-left of your board. This is the one I was trying to refer to. The longer and the smaller pins both should be connected.