You've probably got clogged jets. If the top of the burner is removable, remove it. Mine gets a white build up around the jet holes. A dry brush will flake it offf. Be sure to pull out from the burner, not in or back and forth to the keep the burner free from debris.
My area is switching over gas supplies to a lower BTU mix as the high quality sources are running out. I think the extra filler in the gas contributes to the white crud. I didn't used to get it on the old gas mix.
The old side towel over the burner trick always worked for me . As said clean out the burners, maybe call for a tech. to do maintenance and adjust your burners. I also will invert one burner on top of the other and burn it clean.
Same thing has happened to me a long time ago. My stove still makes that "clickety-clickety-clickety-clickety-click" but only one of the burners lights. Know what? I just keep using the barbecue lighter. Not a big deal, really. (Besides, I found a place where I could get those lighters very cheap. )
I keep some bamboo skewers on the shelf above the open burners.
Our air make up system is notorious for snuffing out the pilots.
Previous line cooks I've employed have turned the burner on and banged a saute pan downhard on the cooktop to ignite the burner, but needless to say, this approach plays **** with the pans as well as everyones nerves on the line. Cheers!