Fuel, air, Compression and ignition are all it takes to make an engine run. Start by checking the basics. Is it getting a spark? Plenty of compression?
Some newer engines have a murphy switch in the crank case that will kill the engine if the oil gets too low. That switch can quit working.
It could have fouled the plug.
It could be a number of things. I'm pretty good at fixing them but not the best at explaining how to do it. Sorry.
Hope this helps at least a little.