central locking wont work on my vauxhall omega?

hi. can anyone help me, i have the original key for my vauxhall omega but the central locking will not work, i have tried the normal way of putting key in, turn till the lights come on then press key fob but its not working, Ive been told that I need to have it tuned in for £25 I thought that was the same as Ive been trying, any hints would be appreciated.