My driver side door lock no longer
react to the remote. I have use the
key to unlock manually after disarming.
The other three doors are fine though.
Any idea how to fix it? Thanks.

lock motor
 

take off the door panel and take a look to ensure everything is still connected. If if is the motor that opens the lock might be burnt out. Since the door opens with the key it seems like the mechanical working are OK. Try testing the motor with a meter or switching one from another door.