Look into the exhaust pipe of the furnace to see if there are wasp nest, dirt dauber, or spider webs. If the exhaust is blocked the furnace will not run.
Inside the furnace there is a switch (called a sail switch) that will not allow the furnace to ignite if there is a blockage in the duct. The way it works; the fan blows against the sail part of the switch which moves the electric contacts into the correct position. If lint, hair, or any trash that gets into the ducts builds up on this switch or is preventing air flow it will not allow the furnace to ignite.
circuit boards in the furnace go bad, sometimes they need replacing (I had to replace one in my Safari not long ago, because I was having the same issues you describe)
I learned enough by reading on this forum and looking at u-tube videos that I was able to remove and clean the sail switch and replace the circuit board on my furnace.