The remote locks and unlocks all doors except the driver side, only the key can be used to do that with this door. If the key is used to lock, then the remote cannot be used to unlock. From the inside, the master door lock switch also works with all except this door, but pressing the lock tab on this door locks all doors.

I think you will have to start looking at the wires that go into the door by the hinge it could be a simple broken wire but you might have to remove the door panel to gain access to the locking solonoid by the door lock and check for power to it when operated, or the link that connects it having fallen off. (if fitted with a link, but normally are). No power to the solonoid is probably a broken wire or dirty connection, power but no movement is probably a stuck (seized up) or burnt out link/lock/solonoid.