You should be able to hear the furnace ignitor clicking away when attempting to ignite the fuel. If you do not hear the clicking of the ignitor it's possible there is a problem with the ignition circuit. First, check the sail switch, then take a look at the high-voltage ignitor circuit. You can usually check the relay for the ignitor at the circuit board and see if it's supplying power when it starts up. If so, but the ignitor is not firing, it's possible you have a bad ignitor coil.