On the display,,is it showing an error message ?,,some units will,,, some will not.
There are two approaches you can try,,although they are not always successful.
The first is to disconnect the positive and negative cables at the battery,, wait 30 min. then reconnect them,,the cd computer may re-boot,,,be sure that the cd player/radio is off,,and the key is not in the ignition.
The second is to remove the positive and negative cables at the battery,,then remove the cd player/radio from the dashboard,,and disconnect all of the electrical connectors on the back of the unit,,wait 30 min,,then reconnect them,,install radio,,then reconnect cables to battery.
This type of problem has known to happen when an unformatted-unfinalized and or uncompatible cd disk is attempted to be operated in the system.
If this does not work the dealer tech can run a diagnostic on the system.