Hi all, after some advice. I've got a sliding back door, normal UPVC thing. annoyingly, the lock has decided to break somewhere in that the key no longer turns. I can remove the key but cannot unlock nor open the door. Anything I can do myself? or do I need a locksmith? I'm assuming I just need a new cylinder but I've got to get the old one out and unlock the door first - anyway I can do this myself? i.e. take out the key and drill somewhere? I don't want to make matters worse/more expensive but if I can do it myself I would like to. I can't open the door to remove the cylinder so everything needs to be done with the door shut and locked.