Help unable to change source to CD Player ?

Hi I have a renault Megane convertible with a 6 cd changer in the boot. After changing a CD the unit now will not work. When i change the from radio to cd using the source buttons the cd player message does not appear on the screen where it used to. I have removed the cds and cleaned them but still nothing. I have reset the unit (using the reset button on the changer) all to no avail...
ANy help please>