12 disk changer in-op (shit's broke)

I have a 96 jetta GL. It's got a (I'm assuming) stock pioneer 12-disk changer; connected to a pioneer tape-deck/removeable face. The source button on the deck switches it back and forth from the disk changer to radio; however, I never listen to the radio, so I don't use the button. But, one day after work, I got in it and it was on the radio; and the source button wouldn't change it to the disk-changer (pist me off bad). it's not the source button itself and the disk changer is still getting power -so I'm assuming it's not a fuse.

it sounds like something in the HU has gone bad that wont activate the CD function