Does it say "safe" on the display? if so then you need the reset code. If you bought the car new or from a dealer you should have been given the code when you bought it, if you weren't then if possible go back and ask for it. If this isn't an option, you need to go to a Vauxhall dealer with the V5 ownership docs, and they will whip out the stereo for you, get the serial number off the back, and ring up Vauxhall for the code. This will cost you �20, bad luck. Just had to pay this myself thanks to mechanics who 'accidentally' disconnected the electrics for no reason when it was in for some bodywork, nice one.