I am trying to get my lawn and flower beds ready for the winter and I tried to start up my Troy-Built mulching lawn mower and it refuses to start. I have changed the gas, checked the oil, changed the air filter, checked the spark plug yet nothing is working.

Do u have spark? After that remove the carb and clean it

I agree, what did the spark plug look like when you checked it.
Wet , dry , black , brown , gray.