Some of this you may already know, so I won't pretend to know everything:
Connecting the doors to the body of the car are large black "accordion" cords/ hose, that, if you unscrew them you'll see they contain a number of electrical and other connections (power windows, locks, etc) to the doors. They do have notches in them that I suppose you could unscrew with some massive wrench, but you should be able to unscrew them just with your hands.
Inside of that big tube will have be a small 1/8" hose. This is your power lock vacuum hose that runs from the main pump near your right tail light. If any one of those hoses is not connected properly, (at any of the door connections) the vacuum won't be strong enough to pull all of the locks down.
Sometimes when screwing on those big electrical connections (accordion hose) the power lock vacuum lines don't reconnect well.
With the door still on the car, propped open as wide as possible, unscrew that large black "accordion hose" on the car body end. Check to see that the vacuum line (it should be orange or blue and plastic / vinyl) is connected well to the plug on the body of the car. You can actually pull the vacuum line away from the door connection and make sure it's jammed into the opposing connection before screwing on the larger connection (accordion hose) that it is held within.
I hope that my explanation was somewhat understandable.