First off I dont have the same tractor not even close but our PTO start up procedure is as follows.
1- engage rear hydraulics
2- lower the 3-point
3- engage the PTO lever
4- set engine speed.
Our PTO lever will not move unless we have done steps 1&2. So my thoughts are maybe you have missed a step.
Another thing to consider is that the lever is connected to a set of gear cogs if for some reason the PTO and the lever have misaligned the lever may be stuck.
Anyhow just a few quick thoughts on what it might be hope it helps.
Owner/Operator - Advanced Grounds Management.
Trees - Lawn - Landscape