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Check around the speaker terminals and make sure that you don't have any loose metal strands (i.e. from speaker wires) bridging between two of the terminals. That can cause a short circuit and shut the unit off. You can also hit the "SPEAKER" button on the front panel to turn the speakers off, which will shut the internal amps off.
As for resetting the unit, I didn't see that mentioned in the manual. You can unplug it for a while (say, 30-60 minutes) and see if that will help clear things up. That likely isn't long enough to do a factory reset, but it can help remove static charge from the electronics.