Sound goes off but keyboard stays on

While I'm playing, there would all of a sudden be no sound, but the keyboard is still on. I can't change the sound or go to any other mode, because the lights indicating what I'm on go off as well. I restarted it and it would work until I press a key and would turn off again. I thought it was the sustain pedal causing because it would do that when I press it, but it does it even without the pedal. How do I fix this?