A little more information, please. When you press the starter button, does the engine turn over, but not start? If the engine doesn´t turn over, does the headlight dim? Do you press the button and absolutly nothing happens?
I had a similar problem, and it was a broken wire. On my bike, if the wheel was turned to the left, it would start. If the wheel was straight, it would not start. A broken wire would make an intermittant connection with the wheel pointed left. Once the wire was located and fixed, no more problems.