what are the symptoms. can you even turn the key? if not you might have a frozen power door lock actuator if you have power door locks. it's also possible that the pushrod has come unclipped from the key cylinder or from the latch on the door itself. take off the door panel and have a look-see.
My actuator went bad, and using the key ended up breaking the rod that goes from the lock to the latch. I haven't fixed it, will one day when the door handle breaks.
One of my actuators is dead too, and I can unlock the door just fine. I had the same problem you have when I had my 91GT. It turned out to be the door latch. They can rust over time and will sieze up. Get a new one: http://www.50resto.com
i can see the little "silver bullet" thing, it's down so i have no way of grabbing it. it did not fall all the way though, it's just in the lock position. i have electric door locks. can you take off the panel with the door closed though? and no the key wont turn, i can turn it slightly, but if i go anymore if feels like the key will break!
hmm, my driver door acuator continuously chatters as long as the unlock button is held and its quite annoying when the alarm unlocks the doors, the same actuator holds when the lock button is held, and the pass side holds when lock or unlock is used....