thats a good one, start simple, make sure undercarriage is clean, you didn't leave a tree in your axle right? grease the front end, jack up front and move wheels back and forth by hand, if it seizes in a spot, or gets too hard, then it is in the links or gear box somewhere. if not, sounds like power steering, most likely pump, maybe flush power steering fluid before trying replacing parts. after that, diagnosis a pump is a little more difficult, you have to determine if its sending the correct pressure. sometimes if you take the belt off, the shaft in the pump is broken, and turns some, or most of the time, with the belt off if the shaft is broke,you can pull the pulley right off.
hope that helps, good luck