Volvo anti theft radio troubles

Put in a new battery. Son pushed all kinds of buttons. now the radio only displays OFF won't ask for code. Even disconntected battery again and pulled fuse out. HELP

You need to put a battery charger on the car and leave it sit with the key on fo 2-4 hours until the screen asks for a code then you will have to have the correct code from volvo so it doesnt happen again