Dead distributor

If this is the case, try drying out the distributor by leaving off the cap or blowing it out with warm air (carefully).

One quick but not all inclusive check would be to disconnect the ignition coil secondary lead (the one that will knock you on your butt) from the distributor and place it near the frame of the vehicle so it can make a spark, then, WITHOUT HOLDING ONTO THE WIRE, crank the engine and see if there is in fact a spark. OR
You could take a samll test/continuity light and hook the ground lead to the frame of the tractor and hook the other end to the plus (+) side of the coil. With the ignition turned on you should have the light come on, if it doesn't, you have no power to the coil. If it does, then hook the test light across the coil leads (one to the plus and the other to the minus) and crank the engine. The light should flicker each time the plugs are supposed to fire (it may be very dim because the spark pulses are very short).

Remember that each time you crank the engine the coil "May" make a spark. You probably have heard of what happens to people who touch things that make sparks when those things don't want to be touched...