post a model number.
which access panel? i'm thinking that you reset the furnace by removing the blower access panel; there's a safety switch in there which cuts power.
turn on the furnace with the top access panel removed (assuming it's an upflow) and carefully observe it. board may have a diagnostic led.
if it by any chance has one of those honeywell smart valves, i can't help u. heard they're a pain in the neck.