ok, so normally you would twist the handle clockwise and then cycle the handle up and down to raise the pad (the part that touches the car)
and when you want to lower the car, you twist the handle counter clockwise and the pad goes down.
so if i am understanding this, you can twist the handle clockwise and it does nothing?
does it stop turning or does it just keep going?
after re-reading your post, i am thinking that when you bring the handle down, the little 'button' it presses down on stays down.
that would either mean the jack leaked out its fluid due to a bad seal or it cant build up pressure due to a bad seal.
there should be a port with a plug in it you can take out to put fluid in.