Gary, can you get the knob to turn all the way to on?
For testing purposes you can use a small torch to heat up the thermocouple at the pilot light
to allow gas to flow to the main burner. By small torch I mean one of those butane soldering things or something a crackhead might use.
You heat up the thermocouple at the pilot light then turn the gas on and your main burner may light. But be cautious about it. If so, Dave's suggestion above might be the answer.
Mine was giving me troubles once and I used one of the long BBQ lighters in at the pilot light, heated it long enough to get the main burner to light. Once it did, I could see the flame from the pilot go from orange to blue as a bunch of carbon type crud blew out. Then a small adjustment to the deflector at the pilot light fixed the thermocouple problem of not getting enough heat. After that it started working like it should.