You don't have a fuse problem if you hear clicking when you turn the ignition. The clicking means that you are just not getting enough current/amps to the starter to get it to operate. The headlights draw quite a bit of current as well which is why they are not working.
If the BOOST switch won't allow the starter to operate, start by checking ALL of your battery connections. You may also have had a single cell go bad, which will drag down the output current to the point where it will not power the starter. A bad cell will sometimes show up in a much lower voltage reading.
When using the BOOST switch remember you have to hold it down while you turn the ignition key.