Is you headlight on all the time the ignition is on? If so, when you hit the start button, are the lights dimming a little, not at all, or practically going out?
I would start with the battery. I don't know how many car batteries I've had over the year that just went dead with no warning. If you have a volt meter, you can throw it on the battery. It should be around 12 1/2 volts. When you hit the starter, if it drops below about 11 volts your battery is probably weak. Below 9 or 10 and it's probably shot. If you don't have a volt meter, Batteries Plus or a bike dealer should have a tester.