The two switches that will keep it from starting are the clutch switch and the pto switch. The are both four prong normally open, normally closed switched. You can take a multimeter and test the switches, Two prongs will have continuity with the button up, and the other two prongs will have continuity with the button down. I haven't looked at the parts diagram for your mower, but if this is the one with the single deck engagement, height lever, try pulling back on the lift lever when trying to start the mower.