Polk sourroundbar no sound

wpipes80

Have had thus sound bar for a few years now. Over the past 6 months when it turns on or unmuted there is sometimes no sound. The only thing that seems to get sound back is to flip power switch on unit or unplug from power. Doesn't always come back on. Have left it unplugged for days with same result. Have replaced optical cable. It powers on but no sound. Flipping sources doesn't resolve