In April 2007 I purchased a Marantz 5-CD player CC4001 and Marantz PM4001 amplifier to replace older equipment. A couple of months ago, when playing my system at a high volume for an extended period of time, the amplifier suddenly went into mute mode. Since then I have been unable to get it to play at any reasonable volume. Even at low volumes, it goes into mute mode midway through a piece of music. The cd player continues to play, but with no sound. It seems like some sort of override was activated at the very high volume, but I can't find any switch to remove the override. I have found no reference to this problem in the manual and am at a loss as to how to correct it. Has anyone else experienced this. Any advice will be gratefully received.