The radio powers on but there is no sound. No CD changer found.

Your sound system is connected via fiber optic. If one component is offline, fuse blown, etc, the entire system goes down. I would disconnect your battery once more and check again. If the sound still doesn't come back, you have an issue with one of the modules. This can be Radio/NAV, CD Changer, Teleaid, Bose Amplifier, Phone.