Write a list of all the possible codes it could be, this might help if you know what it starts with / ends with. It might take a while, and then, try them into your phone. If this doesn't work, put a different SIM card in. When neither of these work, you'll have to ring your network e.g. Tesco, Virgin - media... They'll sort you out. Hope this helps! By the way, if it says you have 3 attempts left, 2 attempts, don't try it, it'll completely lock you out, best call your network if that happens