Is the CD Changer remote? i.e. the CD's are NOT stored in the HeadUnit itself?
The radio communicates with other parts of the entertainment system over the CAN Network for the vehicle. So if you have a CAN network problem, that could be the cause. You can scan it for codes and see if there is a code for CAN bus or do the key dance and see it displays a code in the EVIC.
If the components that don't respond are internal to the radio, then you may just have a problem with the radio itself.
You could try to reset the radio by killing all the power to it, see if that does anything. Either disconnect the battery or pull the radio fuses, you need to pull the IOD fuse as well to clear the radio's memory. (IOD is the always on power to the radio for it to hold its memory) Oh, and you need to secure power for at least 20 minutes to clear memory and reset.
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