Recently had the engine completely taken out of my 2006 Audi A6. After the mechanic got done, everything works but the radio/screen. Nothing powers on....disc changer works, navigation disc ejects but the screen won't turn on. Changed the Fuze after the mechanic said that they are good and still nothing. Any tips? Taking it in to an Audi dealer in a week but was trying to see if anyone could help in the mean time. Thanks!