I don't know if you checked this but look under the midi settings and see if local control is on or off. To hear sound with the keys it should be (on). I don't know if you can turn the main chanel on or off under the mixer, but make sure that is not muted.
GEAR: Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller). SOFTWARE: Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.