I recently got a 2001 BMW X5 3.0 my dad handed down to me. The only problem is the Nav and the radio don't work. The screen is blank and flickers. I know there use to be a sound system in the car that was taking out, and the alternator and battery was replaced. I'm not sure if that has anything to do with it but i checked the wires on back of the nav drive and all the wires are connected and I checked the radio and nav fuses and they are still good. I really don't know what else could be the problem and I'm trying to stay away from taking it to the dealer if possible. Any help or advise as what could be causing this?

Thanks