Small Engines (Lawn Mowers, etc.): Craftsman Lawn Mower repair, craftsman lawn mower, briggs and stratten

Question
We have a Craftsman Lawn mower, with an 11HP Briggs and Stratten motor. While cutting the grass the other day, the belt came off of the mower. we shut off the mower to replace the belt and now it won't start. When trying to start the machine, it backfires once, but doesn't seem to be firing although it is getting spark and getting gas. We took off 2 safety switches and had them tested. One was okay and the other one wasn't working so we replaced it. After reinstalling the switches, the machine still won't start, but is still getting gas/spark.
Would there be any other safety switches? Where do we start? Your input in regards to this problem would be greatly appreciated!! Thanking you in advance for your efforts.

Answer
 Hello Colleen:

 There are 4 Safety Switches. The Seat, Clutch/Brake, Blade and Neutral Safety Switches. Did you Tilt the Mower to Replace the Belt? If so, How was it Tilted? Check the Engine Oil for Gas Smell. Remove the Spark Plug and Set the Throttle to Low. Turn the Engine Several times to Clear the Gas from the Flooded Engine. Replace the Plug with a New Plug and Try to Start the Engine. If you have Fire to the Plug, then the Safety Switches are Working. It May be that the Engine Became Flooded while the Belt was being Replaced. Hope this Helps. Let me know what Happens, Please. Thanks.

 Good Luck

 Respectfully

 John