It may be something as simple as a spider web over the gas valve. you may have to remove the outside cover to gain access. What I have done in the past to remove webs is to blow air thru the furnace exhaust and out the combustion air port and then reverse it has worked for me. You might try standing bey the furnace (outside) and then have someone place the stat in the on position and see if you can hear the spark ignition. If it has gone into lock out remove all power from the furnace for a few seconds to reset the gas valve.
Jake my sidekick (yellow Lab) 10/04 - 05/20
2017 RAM 2500 CC 4X4 Cummins Diesel
2016 Flagstaff 26 FKWS
AF&AM & El Korah Shrine of Idaho