CD Changer and Aerial

[RacingR]

New member here, lots of great info on here!

Purchased recently an A8 4.2L, 97 Model with CD changer in the boot. Everything was working fine for a while, and all of a sudden it just started saying "No CD". Any common causes for this? anything to look at specifically before others?

Also while a not huge, its a pain in the ass, but the aerial has never extended and retracted the whole time I've had it. .... cant hear any motor going to make it go up/down when turned on. ... Can manually put it down by pushing it, but it then gets a loud beeping through the audio system (RDS system?)

Easy to change the motor over?