Can anyone tell me the how to get a door lock working again which has ceased up and will only let me turn the key part of the way. There is no difference if the door is open hence it is not a door alignment problem.
Try using a 'Graphite' spray (available from most DIY and/or motoring shops). A quick squirt through the keyhole, then insert & withdraw the key a few times before trying to turn the key in the cylinder - this usually cures most lock 'seizures'.
I find WD40 left to soak overnight usually works. Give it a really good spray thro the hole and let it soak. Obviously, if the lock is broken, there is no option but replacement.