While not trying to take anything away from stryder's excellent advice

, if the bike is trying to start as soon as the key is turned on, and it doesn't stop trying even when the engine is running, it is probably in the switch pod on the handlebar.
The way to test, albeit I don't know exactly how per se, is to disconnect the start button from the circuit to see if it happens. If it doesn't, then momentarily touch the connections and see it it tries to start without engaging the button itself. If it does, then your button is faulty (stuck on).
Dave