if you can put her in 1st gear, and pto in gear, and let out clutch and pto spins and tractor don't move.. clutch is ok.
unless it has a post aux tranny like a howard or everette that is in neutral.. the next things it could be are:
sheared ring gear rivits
sheared pinion coupling tube
stripped pinion or ring gear
IF you truly can hear the ring gear turning, and could verify that.. then.. broke axle is the most likely cause.
mind you broke axle includes striped splines too..even at the hub.. etc..
others may have more ideas. that's what I got at this moment..