If you are referring to the door lock actuator I will bet that you will find that the rivet that holds the bracket to the door has failed or begun to fail. Once it does fail the motor basically moves up and down and does not actuate the linkage.
You can replace it by going to a local body shop and let them put in a new rivet. These are HUGE rivets and require a special tool. If that is what you want to do pull the panel and do most of the work yourself. It should only cost you like $8.00 that way.
Or, use a 1/4 in nut and bolt in place of the rivot....