You may need to reset the stereo. Try pulling the fuse or disconnecting the battery for a moment. But its more likely the cd player is done. You can get a new stereo but you would need to drop money into the metra kit to retain all of the dic info and settings. The car will work without that. You just can't go through the info or change settings.
You can easily get another working G6 stereo in there and everything will work. You'll just need to get the hu programed for you VIN. Any dealer can do it.