HELP switched to flowering HPS and it stopped working after half hour!

Ok so i switched my bulb to a 600w hps from cfl's and used my ballast i used with no problem last grow. However after 10 mins the bulb was flickering then a further 20 it turned off! It's a new Son-t bulb so i doubt its that so points to the ballast- the bulb wouldnt switch on at all if it was broken right? However when i put my hand on the Ballast i didnt feel a noticible hum or much heat. Plus its a huge ( i reckon old )
Cannatronics one i bought of ebay last year. So is it this or something more simple?

just keep the cfl's on there for 12/12 till you figure the situation out..check the cords maybe a short, the bulb might just a defective one or the ballast just took a shit on ya..just make sure to keep the light on as usual and figure the problem out and then put it back in once fixed or replaced

is it a digital ballast???
My digi ballast blew two bulbs before HTG decided to tell me they wernt compadable.
They replaced them with three sun masters so i cant complain.

no its not digital- its a huge metal housed thing that looks like it was pre ark!- just tried it again- light stayed on a minute then went out- put hand on ballast and can feel nothing- im sure it made a slight sound/ vibration last time i used it. Plus i got an expensive son -t bulb from phillips not a cheapo brand so im thinking ballast! Bloody thing!