As others have pointed out, if the lock turns, it isn't the key.  Disassembling the lock will not get you anywhere, either; the lock is working.  Others have pointed out possibilities, I'd like to add another.  The tailpiece cam that is on the rear of the lock is what actuates the latch mechanism.  If that is broken or has simply come unscrewed from the end of the lock cylinder, that would prevent operation.  The others are correct in describing the access process.

Steve Sandlin

Registered Locksmith

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