1999 Ford Taurus door lock jammed

While holding the hand-operated door handle to simulate opening the door, stick a small rod (#2 phillips screwdriver? ) Into the door lock mechanism (door jamb) where the door-pin would engage, and pull in towards the car to simulate the door opening. Chances are the little clip inside the doorjamb clicked to its locked position after opening the door. Either this is a freak occurrance, or you need to lubricate the locking mechanism. Or search for a fault inside the door such as sticky hinges, bent rods, etc.