When I pull the pto switch to engage the blade the engine will shut down.blades turn freely by hand. Acts as if there is safety switch grounding out. Seat switch still works but can't figure it out.

Hi,
It sure sounds as if it is in the safety circuit of the seat, the description is that of a bad seat switch. Cgeck for broken wires. Cannot go much further without a model number. Some machines use the ground circuit in strange ways.
Peace,
Clarke