Subaru Outback 2010 Change of Radio

[Outbackman]

I have just fitted a replacement radio (Panasonic 86201AJ301) for which I have the Code, however the screen isn't asking for the code but instead is showing the word "Security" on the screen.

Nothing seems to activate a change of the screen. How do I get to input the code.

I have disconnected the power and the radio has worked but then after about an hour the radio goes off and reverts to the "Security" error showing.

Any ideas please

Thanks Graham