11 plate Fiesta radio problem after batt change

[Landshark]

My wife has an 11 plated Fiesta Titanium with the Sony audio system. We've recently had to change the battery as it kept going flat.

Since the change the radio/Bluetooth etc doesn't work, all it does when you turn it on is show the Ford badge and 'Audio' written underneath! If you turn it off it goes back to time & date?!?

How do I get it working again, there's no prompts for any pin and the manual and internet offer no help.

Any ideas