Why does My radio don't work?

I have a Kenwood KDC-MP632U with a 6 CD changer and all of sudden the radio audio does not work..The message display doesn't even work when I bought the vehicle.but the background illumination does..Uhmm whats wrong. I tried disconnecting the radio from its harness twice but still nothing..and also the main radio fuse is ok..what could be the problem? The vehicle is a 2007 Chevrolet Silverado 1500 Clic WT.