Have you checked the associated fuses? There are 3, Radio No1 (20A located in engine bay fuse box),Radio No2 (15A under dash fuse box) and Dome (10A engine bay fuse box)any of these would affect the display and audio system if blown. The first 2 also supply power to the CD changer so if that is also not working check the fuses.The fuse box covers normally have a list of the fuses and positions attached to them.