Sounds like a sticky control valve or a broken fork retracting spring. Try lifting a light implement (like a back blade) then shut down. Assuming the implement doesn't lower when the control lever is moved downward, remove one or both of the inspection plates and carefully move the control valve by hand. Be careful not to disengage it from the yoke or to pull it all the way out of the pump. The valve should operate smootly and easily. If the implement drops when you move the valve by hand and the valve wasn't hard to move then something's gone wrong with your linkage. Just be careful not to stick your hand in the pump housing with the tractor running -- the PTO shaft runs through the control fork and through the pump.
Hope this helps,
Pete P.
Harborcreek, Penna.
