3cv

I am a blow in from Tasmania seeking help with issues with my 2006 C5 Hdi. When I recently removed the battery leads to charge up the battery I found that the radio would not work when it was was reconnected. The radio on the display is now 'greyed' out and there is no way to access the settings. Other than take it to the dealership and get charged an arm and a leg I was hoping someone might be able to suggest a fix? If it is a technical issue with the radio is it possible to replace it with another from a C5 or even a non OEM radio? Other ECU issues include a regular alert to say the 'depollution requires attention' when it is just as likely to vanish as quickly as it appeared, LHF tyre is low on air when I know it's not and none of rear seat passengers have safety belts fastened when I have no passengers in the rear. Any assistance much appreciated.