In light of earlier posts in this thread. I'd check the valves. Because something happened to just make it stop even trying to start.
Just curious, but what method was used to verify the spark? Today's engines run with way more powerful spark than they used to.
Some older testers, and methods aren't able to verify there's enough power for it to start the engine. Only that there's actually a spark.
I use a tester, that looks like a mini spark plug. There's a large gap. If the spark jumps the large gap, then there's plenty of fire to start. They're cheap, and easy to find, and easy to use.
Also they're absolutely necessary. It's recommended that you not just pull the plug, and lay it on the head, to check spark anymore. Bad things can happen to delicate electronics when doing this.