How can i fix my countax c600h?

Yesterday i was using my 10+ yr old countax c600h Briggs and stratton 16hp engine and all was fine. Just before switching off i depressed the headlight switch to try it (which didn't wiork by the way!)and all dash lights went out. Engine continued running ok but after switching off then trying to restart again i still have no lights on the dash and it will not start. All i get is a single click from the engine on turning the key. I have changed the2 spade fuses and disconnected the leads to the headlight switch in case it was that causing the problem--battery connections are tight but still nothing--I cant see any loose wires but all was fine anyway before i tried the headlights. any help as to what it may be causing the problem would be greatly appreciated.