Audio System will not turn on

My 2008 Titan PRO-EX is equipped with what the manual identifies as a type D audio system. Four days ago I opened the car to find a CD ejected and on the center console. To my knowledge no one had been in there but me. When I turned the key on, the radio would not start (no audio or CD functions, or control functions). The accessory power (clock, back light and auto dimming) work as they usually do. I've checked fusses (10 and 15 amp) and rebooted the system by disconnecting the battery. No change. Can anyone suggest what may be wrong or can fix this?