That sounds like the internal detection mechanism for the magazine is no longer working ; either
Microswitch moved / broken (or wiring to it)
Magazine damaged, meaning magazine does not trio the switch
I've no specific knowledge here, and recognise my suggestions may be a little old tech, but it's where I would start.
First job would be to go to the CD changer and physically remove / replace the magazine - that might be all that's needed.
ps - this should be in the classic 9-5 forum, if a mod can move it