If it's one of the two-strokes, I keep hearing how the kill switches can be a pain also. I replaced mine with a toggle switch from Radio Shack right from the beginning so I've never had to deal with it, but I've heard other people having trouble with the cheap ones shorting out or failing to work at all.
Have you pulled the plug and, with the cable on it, held it to the head to check for spark? If not, the plug and the kill switch are some of the cheapest fixes you can do.
I use my choke to kill the engine. I accidently broke a wire from the kill switch so only the black wire remains in tact. I put the spark plug to my engine and pushed and saw no spark for the plug. So I assume that's the problem unless this is not what you are asking me.