Windsheild Wiper

My driver side windsheidl wiper recently stopped working. The passenger side one still works fine. When I tried to take a look at it, I noticed that it could move freely back and forth w/o the car on while the passenger side one couldn't be moved much at all. Any ideas?

The nut on the arm pivot is loose, there is actually a plastic cover on the pivot end or possibly a button cover that hides the nut that holds the arm to the pivot shaft, lift it up or remove it from the pivot end to expose the nut, poisition the wiper arm where it should be on the windshield (Make sure the wipers are in the off or park position) and hold it in place while tightening up the nut on the pivot shaft then close the cover.