Check the internal speaker line fuses.
7 responses Add your response
The amp does have a relay that mutes the output at initial turn-on for 3-5 seconds. It might be if you are turning it off then right back on, the relay hasn't had time to reset. Try leaving it off for a few minutes, then turning it back on.
Also, like Partial stated, it could be a faulty power switch and/or relay itself that is causing the problem.