When I turn up the stat the inducer blower comes on,the ignighter glows and I think I can here a click from the gas valve.but that is it.It is about 10 years old.It did this last year and I went out and tapped on the gas pipe a couple of times and had no more trouble all last winter.

If the unit has a flame sensor clean it with steel wool or sandpaper. Or you can test it if you have the proper meter. This is the cheap fix if it works.