This might sound stupid, but it happened to me. My shut-off was located in the lazzarette. After pulling the shut-off to turn off the engine, I failed to push it back down to the running position. The next time I tried to start it, it wouldn't start(duh!). I went through a lot of the things that you tried with no luck, until someone suggested that I try to go through what I did the last time I shut the engine down, and it became obvious. Because the shut-off was in tha lazzerette, I never thought of looking there first.