The first thing you will need to do is try lighting the burner manually with a match or bbq lighter. Bring the flame next to the burner then turn on the griddle knob. It should light up. If it does then it is either a weak spark on the ignition system due to debris on the electrode or there is blockage in the burner eyes at the electrode. Try poking out the eyes of the burner with a safety pin or sewing needle. And try using a wire brush to lightly clean the electrode head(where the spark comes from). If your tried lighting the burner with a match or bbq lighter and it did not light or a very small flame came out then there is a restriction in either the burner eyes, venturri, or burner orfice. Frist inspect the burner eyes for any blockage(grease or particles of food) and then use the sewing needle or safety pin to clean out all the burner eyes. If the burner is easily removed then go ahead and remove it and check the venturri(burner pipe) for any debris inside it. A small bottle brush can be used to clear the venturri. And finally with the burner removed you should be able to see the burner orfice. It will look like a small nut(usually brass) with a very small hole in it. This is where the gas comes out and if this hole becomes plugged then the burner will not work. The best way to clear this hole is to use a very small wire like the wire on a sandwich bag tie strap. Burn the plastic off of the tie strap to expose the thin metal wire and then use the wire to clear out the hole. DO NOT USE ANYTHING LARGE to try and clear out this hole. It is tiny for a reason and the soft brass can be opened up easily while try to clear the orfice hole causing a huge increase in gas pressure. If you clear the orfice hole and still do not get any gas pressure then the next step would be to remove the orfice(this requires a orfice wrench) and verify that you get gas coming from the burner tube with the orfice removed. If you do not get any gas after removing the orfice the more than likely the problem lies with the burner valve restricted internally and will need to be re-built or replaced.