Mercedes Benz 2009 S550 4matic No Audio sound


I'm having problem with my 2009 S550 4matic. When ever I tried to play something on my system no audio is coming from fm/am, satellite radio, CD player or DVD. I have changed both the battery. Still same issue. All the buttons are working display screen working to. But I'm getting no sound out of my speakers. I have Harmon Kardon 7.1 in the car.
Please anybody can help.
What is this problem how we I can fix it
Thank's in advance.