I mowed the yard with no problems and parked the tractor. I came back a week later to mow and the PTO won't engage. Tried moving the PTO position selector from rear to mid to both with no change. Inspected the lever which seems harder to move than I remember. NOTHING!!! The mid and rear ptos turn and I don't feel any grinding. I"ve scoured the interned and looked in the service manual. The manual just appears to jump to pull the transmission and take apart. POINT me in the proper direction please!!!