I think you've solved the problem yourself. It sounds to me like the linkage that connects the lock actuator to the actual locking mechanism is broken, or that the gears (if it has them, I don't know if this car uses a solenoid or a motor with a gearbox to lock and unlock the doors) in the gearbox are stripped. There is no difference between the actual latch on a car with no power locks and one with power locks. There's a linkage from the manual actuator (the "button" that you pull on to unlock the door) to the latch, and the power lock system acts on this linkage to lock and unlock the doors. You're going to have to take the door apart to see what's what.