C320 CDI Sport W204 Radio/CD locked in CD mode.

[pugilist]

Hi all,
Have owned a MB for a week. As mentioned above it is a C320 CDi Sport. Just learning the ropes with it and still finding my way around. So far very pleased with it. However today I could not select the radio, telephone etc on the system as it is locked in the CD player mode. Any help would be appreciated. This could be embarrasing if it is a function select problem due to my naivity

Thanks.

PS hoping for a response as I have had none on my earlier posts.