I have a Troy-Built Poney mower and it has been doing fine till this weekend when I tried to start it, it would not crank. Its getting gas, and backed fired once. I checked all safety switches and all seem to be OK. What's next?

Need to clarify a few points, for most of us cranking means the engine turns over, you can hear the starter rotating the engine. Does you engine rotate, crank, turn over? How are you testing your safety switches? Does the engine get spark? Which engine, brand and model do you have?