Which PTO shaft are you using? The 1 3/4" 1000 rpm? Or the 1 3/8" 1000 or 540? If you are using the 1 3/8 shaft I am guessing you might have sheared the drive collar. It is part #9 in the attachment. The part number is R270864. Just remove the 4- #1 bolts and remove the pto adapter assembly to access it. If that is not the problem then I am guessing an electrical problem - bad switch, solenoid, or loose wire maybe. Are you getting any error codes or warning lights?