Door not shutting

Hey guys on my 73 'vert...heres the deal, the door used to shut fine. Now its not. The two "clamps" or whatever you would call them will not open up to accept the knob on the body of the car. You cant force them up with a screwdriver, nor will locking/unlocking the door. Unlocking or locking it moves the rod that comes out of the door panel, but doesnt move the clamps. The door will shut, but you have to absolutely SLAM it to get it to stick. Obviously I want this taken care of but I'm not sure what could be wrong. Also, it looks like it would be one hell of a job to try to take it out of the door, once you got it from behind the glass, you'd have to disconnect the rods and pull it through behind the door panel? Anyone else have any similiar problems?

No no, the mechanism is jammed. Its not supposed to be clamped shut when the door is open right? Obviously I cant tell what its doing when the door is shut, but the door does shut if you slam it really really hard, so I guess its biting a little bit. I will check it out later today with your advice krash.