Protect is across the screen - Kenwood KDC-MP332 CD Player

I'm guessing you have a kenwood... you will have to get to the back of the radio and unplug it for a couple of minutes then plug it back in.
this happens when you turn the volume up too much or you have a blown speaker (may hear it rattling around and it probably sounds ok at lower volumes) that is registering lower than nominal impedance around 3.8 ohms or so. if you have recently installed new speakers and this is happening it is possible that one of the speakers' terminals is resting on the metal area of the door or rear deck or a speaker wire has been drilled through during installation. this will cause a drop in impedance and therefore result in the same symptom you are experiencing.