Does the key turn in the lock or does it not even turn at all? Can you lock/unlock manually from the inside? I'm thinking that you have a broken or disconnected door lock rod but you'll have to get the door panel off to be able to see.
2004 Sable LS Prem DOHC
2001 Taurus SES DOHC
Previously owned:2000 Taurus SE, 1994 Sable GS, 1988 Taurus LX