Check the crank position sensor.
It tells the ECU that the motor is turning and to fire the plugs. If its not working or sending a weak signal the ECU doesn't know if the motor is turning or what position the crank is in rotation. There should be a plug with two wires running into it up by the butterfly valve under the plastic engine cover. You can read the signal to see if its working. The check procedure should be in the Montero FSM. The actual sensor is down by the crank pulley in the front of the motor. If I remember correctly you have to pull timing cover and belt to get to it I think.