Its according on how new.Still under warranty ,take to shop and let them worry about it.If not,you could start by isolating the wiring,sounds like I would start at the switch to the headlight.multimeter would be idea,when switched on, not running,check for voltage at the bulbs.Dont know if these bikes have fuses,more then likely,check them all first.If the bike is old but new to you,I have read around here about people doing headlight/turnsignal mods so as to switch them on and off while bike is running.If you bought it from someone, maybe they did it to that one.In that case, check around through search tool for headlight mods and you may be able to reverse the mod or locate the source of the problem,ie..a switch somewhere.At any rate some one here more knowledgable then I,will give you some better advice.Learning new stuff everyday about these bikes myself.
Hope that helps,
Whiteboy06