You, my friend, have what is known as a can of worms. Hold a long shank screwdriver to the cylinderhead and within 1/8" of the sparkplug. Turn the engine over, with the key or spin the flywheel. Do you get a spark??? You may have to do this 2 or 3 times if you are not in a dimmly lit area. If the Ignition is on you should get a spark of sufficient amplitude to light your fire. If not, eliminate the safeties. Disconnect the magneto kill wire and try again. It's on the side of the engine usually by the governor arm. The engine may start so be carefull. If not reconnect the wire. If this was the first run of the season take the float bowl off the bottom of the carb, but be carefull not to tear the little gasket if it sticks. You may have water, gum, dirt, etc. in the bowl. dump it out and wipe it out with a cloth. Get a spray can of carb cleaner and spray where the bowl was on the carb. Then pull the fuel line off the carb and spray carb cleaner into the fitting to the carb and wait. Do it again until you see it dripping from the carb where the bowl was. Put the bowl back on and spray carbcleaner down the throat (where the air goes) of the carb. Try to start the engine like a cold start, not a warm start. It may only run on choke at first. If so spray short bursts down the throat until it starts to smooth out. Go mow the lawn if it is running, but only at 3/4-full throttle until it is all done and spray for 8 seconds into the gas tank also. If none of this has worked you could have a lot of carbon buildup in the cylinder, or burned valves, a blown head gasket, or if you forgot the oil a siezed engine.