first make sure that the actuator is indeed trying to unlock/lock the door...if not then look into the wiring...apperently famous on some cars to bend the wire too much in the door opening motion.
i had this problem back at the end of summer ( a much better time to have a problem with door not locking/unlooking!), on my passenger door. it occoured after me and my g/f played pull the outside handle and lock the doors game... really funny, but not worth all the agrevation it causes! i had to get a new (well, used)latch and lock actuator from the wreckers (from any taurus with power locks).
now pull your door panel (watch out for one attached light bulb assembly...the wire going into the door), with the window all the way up, take the nuts off of the regulator slide track right in front of where you need to go...2 nuts, and then weasle and swing that slide track off of the one end, it pops off without much of a fight, and goes back on easy. then you see what you have to do, 3 screws tightly (make sure you have the perfect fit screwdriver, or socket end i found easy onto my ratchet...also get spares from your junkyard when you pull the other)...just becarefull with the actautor rods that go to the inside of the outer door handle and lock(dont bend them too much/out of shape or you will have troubles with your locks/door handles later)...you can see which end of the rod is easier to pull out of its counterpart (i cant remember)...if you get really confused, pull your passenger door panel to copy that side. and get new 'trees' to put your door panel back on, or it will be falling off later. they are like $2 for a pack of 3-5. it took me about 2 hours say to do this when i had to get it done...i did try and clean and **** everything before that, but it did not work. i was tired of not having access to the passenger door all the time.
oh and the pwoer lock actuator is really going to piiss you off, so be prepared! it is easiest to 'bend' the actuator outof the bracket...it will pop out...a plastic ring on either side. then unbolt the bracket, and put the new actuator on it...with the bolt in the hole first, and then you should be able to get your finger on that bolt while tightening the nut on the outside of the door. OR you can leave the bracket on and play with having those plastic rings falling all the time...either way its a pain...but you feel better when it works again!!!