Corsa radio stuck in safe mode?

Hi folks I have a Corsa B with the radio (for which I have the code) permanently saying 'safe'. Ive tried holding AS while turning the ignition on etc but I dont get a beep and cant input the code.
Ive tried this radio in my Zafira and it works fine using the AS button to input the code but as soon as I put it back in the Corsa, it just displays 'safe' again. Any ideas gratefully received.