I've reinstalled the original radio in my Peugeot 406, but can't get it to light up on the text display....

When I turn it on the backing lights work, and if I press 6 it tunes into a station and bleeps every 3 seconds, so I know it works, but still no text display, so I can't enter the code (which I still have) to free it up.

It worked fine before I removed it,..

Can anyone help?