John Deere 125a Won't Start?

I have an 2006 John Deere 0125a riding mower that powered down while mowing. I noticed the oil drain tube was gone. We got a plug and refilled the oil and could not get mower to start. We replaced the fuel filter and the 2 armatures as well as new plugs and still can't get it to run. We have spark to plugs and have verified fuel up to the new filter. We have also tried a shot of starting fluid to see if fuel was an issue and it still would not start. We also cleaned the negative battery terminal. At this point I can't remember what else we tried. It is a Briggs 20 hp v twin motor on this mower. There is a strong charge on the battery and fresh fuel. Any suggestion on what to try next?