Headlights not working

All the lights on my car work, except my Headlights. I can only operate my car in the daytime. They were working fine last week. I just bought the car in September from a used car lot. I pulled all the mini fuses from the fuse block under the hood. they were fine, nothing broken or burned out. When I pull out the Headlight knob to the first position, the running lights come on. When I pull out the knob again, the headlights do not come on. Also, I have the Twilight Lever turned off.