Donato:
here is what I do. When the airplane is parked by FSX after creating a flight, it is usually parked too close to the terminal. I reverse thrust and it slowly moves the airplane back. shut down the engines and try the jetway again. if it still wont move, start the engines and move it back further. when you get the plane parked right, they do move. It drove me crazy too. you might be able to slew the plane back or use an FSX pushback command. you have to position the plane just right. And make sure the engines are off and the park brake on. patience my friend, patience.