Symphony Radio

Hello. I've tried to install a Symphony Radio that was originally on a cousin's Superb and I can't get it to work. Mine was broken and my cousin has long replaced his Symphony by another radio. I know the correct code for this radio and have complete info on both the "native" car and my car but I can't seem to get it fixed. It stays with a "SAFE" message on the display and doesn't change to code selection. How can I do this? There must be a button combination to unlock this and let me put the code in it... Any help appreciated,

Joao