I had the same thing. I pulled the outlet and found that one of the wires had pulled out of the connection on the back. Mine doesn't have screws on the back of the outlets like a home outlet does, the wire simply gets pinched in between the terminal, not a very good design IMHO. if it's not that outlet then look at the one next to it, they usually jump from one to another and that lead wire might have come off instead.
Warning, unplug shore power before doing this... 120VAC is shocking!