Check your local hardware store and see if they carry a MH or HPS bulb that matches your ballast. If that new light fails, get yourself some emergency CFLs and get that ballast into the return system ASAP.
Its possible your bulb is bad, but without a different one to try, you don't know and I understand on wanting to wait to be sure of that.
You said that ballast is under warranty. DO NOT TRY AND FIX IT! Don't open it or do anything to it or you will be out of luck because if it looks tampered with, you can't exchange it.
I am in the same boat as you on the exchange, but I was lucky enough to have two ballasts and reflectors. During the waiting for the new one, I am flipping my reflectors with the working ballast every 6 hours during lights on.