I would pump it as much as you can and then quickly open the pressure relief valve. Do this a couple of times. The other thing you can do is this...... spin the handle 5 or 6 times clockwise, give it 5 or 6 full turns, then see if the pump works. I know spinning the handle sounds ridiculous but believe it or not sometimes it actually does fix the problem.... give it a try, ya got nothing to lose.
Jeff