Welcome to the forum foot. If you did not disconnect the battery when you took the cd player out, you might try disconnecting it for a minute and then reconnecting it. That system seems to want to be reset after you add or remove something. Otherwise, I'd suggest one of the connectors you played with is not tight. Also, check your mute switch.
That CD unit is just an accident waiting to happen. There are alot of us that have removed them and replaced them with the plug in style mp3 players that are controlled with the handlebar controls. Much easier and no moving parts to get screwed up when hitting a pothole.