First find the electronic control board. Is the diagnostic light on and flashing a code? If not look for the automotive type fuse on the board. It is a 3 amp. Is it blown? Next look for a screw in fuse in the ssu switch on the side of the furnace. Is it blown? If all the fuses are good is the door switch behind the front cover working? Is the door properely installed? If all these items are working, you should have power to the furnace. If these items are ok, check for 24volts at the transformer. Check the terminals not black and white. If you have voltage there, remove the red and white thermostat wires on the control board. Next take jump wire and jump the red and white terminals. This rules out the stat and stat wiring. Your furnace should start. Check the status light for any further problems and crossreference the flashing light code to fix.