Murray Riding Mower Won't Start?

I have a Murray mower (model 46621X92C) with an 18hp 2 cyl Briggs and Stratton engine. I picked up grass clippings and it was running well. I turned it off and took my leaf blower and blew off the grass. When I tried to start it, the engine cranked, but would not start.

I checked and found that I was not getting a spark to the plugs. I tried several things and the engine would crank, but not start. Then the engine would not crank any more. The battery is good and the starter is good. I replaced the ignition switch. I could not find a broken or lose wire. All the switches seem to be working. If anyone has any ideas, I would really appreciate them. I am at a loss on what to do. Thanks.