HELP WITH 600w hps!

i got a 600w hps ballast and bulb from a friend lastnight, had to re-wire n stuff to get it on. it worked perfect, turned it off n then on again 10mins later. fine, left it for an hour... still working good. gone to set it up in my grow room, nothing. can hear the ballast buzzing a bit as normal but no light. checked the connections, all seems fine. i undid all the wires and put my mh ballast on and bulb, fine. so im out of ideas? any1 shed any light? lol

bad bulb maybe if u wired it right the frist time i think your ok, but if u did't and u shorted the tarnsformer out there would have been a load pop and you wouldn't hear the transformer humming so lead's me to think mybe a bad bulb.. "you only get one try to wire them right because once you shorted the transformer out THAT'S IT and also the ignition too check that could have gone bad............