most likley the acuator has failed. have it tested to be sure

Roy

Are you saying that is will not lock at all or it will not lock using the LOCK button? Can you manually lock it?

If you can manually lock it it could either be a bad switch (try both switches to eliminate this possibility).

If it can only be locked manually, you'll have to remove the door panel to test the actuator. check it for power when the lock button is pushed. if it gets power but does not operate, the actuator is bad. If is doesn't get power, check the fuses and door lock switches. let me know if you need further assistance.