Bad battery or you need to clean the terminals and connectors ! That single click is usually the sign of what I just mentioned . Go to a parts store and have them check the voltage of your battery ! Clean all the connections and get a can of that protective spray . They use such junky connectors now that they corrode easily . The parts stores also have terminal / connector cleaner tools and they are cheap . Good luck and I hope I've given you some help !
Could be anything in the car's electrical system, from a bad battery, to broken wires, regulator, distributor, spark plugs, faulty ignition, etc. Hopefully, it's only your battery, fixing a car's electrical problems can get very expensive!