I am assuming you mean the PTO lever , check to make sure the PTO lever is in the right position, on the BX there are 3. One for just the MMM one for just the rear PTO and one that runs both MMM and the PTO.
When it is in the rear PTO position then when you engage the lever on the right side of the seat the for the PTO and it should work, just make sure someone hasn't bumped the PTO selector lever
Curious, any chance the shredder's slip clutch is ,well, slipping ?
The posting of make/model info of your shredder would be helpful,as not all are made the same way.
and.
What are you 'spraying with water' ?