S500 radio with no sound
 

I just bought this '96 S500 Coupe a few days ago - bought it knowing the radio gives no sound. The man I bought it from had just added a factory 6-Disc trunk mounted changer. AND he admitted to trying to get the factory phone to work with no luck. Radio comes on - cassette plays - CD changer loads - etc. But ZERO volume on any of them.
I remember these models had it to where when the phone rings, the radio goes to zero volume - could PO have somehow activated that? I cannot even get phone to power on.
Please help,
Mark