I've always been told if your car doesn't start always start with the battery first. This includes cleaning your battery posts and cables. You need 12 volts to start your engine, but you don't necessarily need 12 volts to operate the electrical systems in your vehicle (that's why your gauges swing back and forth). If the engine does not turn over and nothing happens it is more likely the battery or the cables. It could be the starter but I would start with what I have already mentioned.