C class w03 -radio MUTED after battery replacement

[HITECH]

I replaced the battery on my old C220 saloon W03. Now the radio comes up MUTE. Anybody any idea why its done this. I havent put diagnostics on it yet To see if it’s something i can reset diagnostically. Just getting it ready to sell for MOT and new owner will require a working stereo.
Can anybody shine some light in this? Its resulted from a flat battery then battery replaced.