On a guess I would say look at the PTO engagement lever, it might have broken off. When you move the lever, does it feel like it's doing anything? With the engine off, if you turn the output shaft does it feel like you're turning anything else or does it feel like it's spinning free?
There's not much to the PTO. To help you visualize it, if you follow it from the flywheel, at the flywheel the PTO clutch is under the drive clutch. The input shaft to the drive transmission is hollow and the PTO driveshaft runs inside of it and through the drive transmission. The driveshaft runs to a small gearbox under the seat that drops the speed down about 4:1, if you have the 2-speed PTO it has two speeds. Then it outputs through the back. So the components that could possibly fail are the clutch, the driveshaft, the gearbox or the output shaft.
It's important to try and isolate where the problem is because it affects how you attack it. If it's at the clutch end you have to split the tractor to expose the clutch. If it's at the gearbox you can get to it by taking off the seat and the lift box. If it's the engagement lever you might be able to fix it from the outside. So the first step is to probe from the outside and see if you can figure out what is connected and what isn't so you know where to start.
On mine it is simple and safe to take off the gearshift cover, four bolts. I don't know how much you can see, but that allows a look inside to see if you can figure out what is connected and what isn't.
Another thing to note is whether with no implement on the PTO, the PTO engaged and the engine running the PTO output shaft turns a little or not at all. If it turns a little that indicates something is slipping.
