OK lets think this through. A 3-point hit goes up by hydraulic pressure. It goes back down by gravity. You say it will not go up or down. One of the few things that will stop it from going down is is the drop rate control is turned off. If the 3-point hitch arms were all the way up and the drop rate control was in the off position, the arms would not move. Now if the arms are all the way down the drop rate control would not affect this.
Do you hear anything when you try to lift the arms?