Does anything play thru the silent speaker? Ie windows sounds, media player, video games, whatever.. If not, it might be wiring or a bad speaker.
If other projects play fine but no tracks on this project play thru one speakers, the main mix might be panned all the way to one side.
If other tracks in this project play fine and ONLY the vox track is coming out of one side, then the track is panned to one side, or as chili said, you recorded to one side of a stereo track.