Ballast or Igniter????

[Blade69]

My "bulb" went out a little while ago. I was waiting until it got a little warmer to change it. Today was as good as any. Anyway, I replaced the bulb, and no go. So now I'm wondering if it's the ballast on the bottom of the casing or the igniter inside. The reason I'm saying igniter is because as I was taking the assembly out, I noticed the cover was completely loose. I guess I over-tightened the screws last year when I upgraded my bulbs and changed my angel-eyes. In short, which one is more likely to be the problem? I know the more experienced guys have come across this before.

Thanks in advance.