Agree with 3rensho. I had the same problem with a previous citroen. It was to do with entering a security code which was all part of an initiative to prevent vehicle (radio) thefts. You will probably need to speak with your local Citroen dealer. Now I come to think about it I had a card with the user manual that also contained the details required for this purpose.
Had problems with a previous car when someone disconnected the battery without thinking. No idea of the code so removed radio with the intention of taking it for recoding but on removal found previous owner had written code on radio in felt tip pen. Switched on entered code and "Robert is your Mother's Brother"
Berlingo Multispace 2.0HDI '54 reg Mediterranean Blue