This'll sound stupid; but please bear with me...

pps:
1. Sometimes my lock won't spin if the key is pushed in either too far, OR not far enough...
Have you tried "jiggling" things around a bit?
2. Could the lock just be gummed up with some sort of "crud?
Have you tried seeing if some lubricant helps?
Sorry... I had to ask the simplist stuff!
Anything else is beyond my pay grade!