not enough info.
the inducer fan is the first step to the ignition process. Does the ignitor even attempt to glow, or int the case that it is spark ignition, does it attemt to spark? if the answer is no, then you probably have an obstruction in the flue or a plug in the air switch tube.
Check to see if you have 24 volts to both legs of the air switch. if you do, then you would have an ignitor problem.
if the ignitor tries to light but there is no gas, then ensure that all gas valves are on, and test the valve for 24 volts. If you have power and gas, then you have a bad gas valve.