switching mh to hps?

ahoy i got a 400w mh a month ago and the light came all wired and ready to use with a ballast box and everything you just had hang it up and plug it in...unfortunately the ballast is a VS ballast that can take mh and mercury vapour...i then organised a VS ballast for mh and hps but when a put an hps bulb in it, it dnt work...what am i doing wrong?there is a tube like object in the ballast box which i think is a capacitor but not sure...i think i myt need an igniter or something?if so how do i connect the igniter?and now i am busy budding with a mh and after a week flowers are showing but is this gonna affect the bus hugely?thanx alot

bud not bus

i wouldn't mess with that unless i hated my house and wanted it to burn down

ya wouldn wana do that,thats y im lookin for help...

try mh conversion lamps

oh nvm you're doing it the other way round. i wonder if there are hps conversion lamps

ya you do get hps conversion bulbs gonna check that out thanx alot