Rally Ride on Lawn Mower Won't Restart?

I'm looking for some help with my Rally ride on lawn mower which has a 15.5hp Briggs and Stratton engine. I was cutting the lawn and the mower just cut out, no warning, as if you just turned the ignition off. I have checked the safety switches and they're fine; there is spark at the plug. I'm at a total loss as to what could be the problem. Any and all help would be very grateful please. Thanks.