UNLOCK CODES FOR CAR STEREO DELKO ELECTRONICS CDR 500 (VAUHALL VECTRA)?

HI

I have just had a new battery fitted to my car and the stereo is displaying a SAFE sign, I have no clue how to sort this out I have tried holding the buttons down to put some of the suggested codes in but it just keeps displaying the SAFE sign and I can't enter any codes, which I also need.

Thanks

Gill