Check your supply line coming from the jet drive to the motor for obstruction. The line can get clogged from anywhere from inside the pump to the motor.
Then check your dump line to see if it is clear of debris.
You may have to remove the pump bowl and impellar to see if there is an obstruction at the pump.
Of course that includes any valves or thermostat that may be closed.
Don't run the engine until you have found the problem.
Kojac