LOSS OF VOLUME ON CD AUDIO UNIT IN FORD MONDEO?

THE BATTERY DIED ON THE CAR SO I REMOVED IT AND REPLACED IT. I THEN HAD TO RE_ENTER THE CODE FOR THE STEREO CD PLAYER ( ITS A 600 SINGLE CD FACTORY FITTED IN A 2003 MONDEO.). AFTER DOING THIS THE STERO LIGHTS UP AND ALLOWS ME TO TUNE IN STATIONS AND PUT CDS IN ETC ALL FUNCTIONS LOOK TO BE WORKING PROPERLY EXCEPT THAT THERE IS NO SOUND FROM THE UNIT THE VOLUME CAN BE SET ON MAX AND I CAN JUST BARELY HEAR IT ??? ANY IDEAS.