I have a gas furnace... when I will hear a clicking sound when the furnace is ready to fire up but it doesn't
I see the pilot light go on but the blower does not not go on either... on the auto setting...

On the fan on setting the blower fan will go on,, the burner clicks but will not fire up...

Brand and model of your furnace?
Does it vent with plastic or metal?
In the bottom door are you getting a flash code?