Without seeing what you have there it is hard to make a suggestion but generally I work backwards with those issues. Fuel or spark. In this case spark so can you pull the spark plug wire off of the plug and see if there is spark to the wire? If so, is the plug bad or the spark weak? If there is no spark, move back to the next component before the wire. Coil or electronic? Bad component? As someone said, rodent damage to something?
You said spark but by any chance could it be bad fuel?