Door Locks

I have a w124, '86. There is a problem with the driver's door lock. When I put the key in the lock button inside goes down but the door is not locked. I also know that this button should not go down unless the door is closed as it does now.

If anybody knows how to fix it, please e-mail your reply to me at: linex2@yahoo.com. because I have no access to the manuals.

Thanks in advance.