If you want to imput the code, first you need to turn the key to the "accessories" position (the very first click, where the radio will come on as well as the OBC backlight). Then turn the radio on, and don't touch it for an hour. Not 53 min, an hour.
Then just imput your code on the radio preset buttons. If you hear a beep before you get to the last digit, stop immediately and start over. You have three tries before the radio assumes you're guessing and locks up again.
Supposably, if you remove all power to the radio, that will also enable you to enter you're code. But it didn't work for me, I had to use the key-in-ignition fur' an hour method.