In January I replaced the bulbs in my 72" fixture, and now 2 of the bulbs aren't working, and also one set of moonlight LED's. My fixture is 72", but each bulb is only 36", so my 4 bulb unit has actually 8 bulbs. The 2 bulbs that are out are situated in line with each other. I'm doubting my brand new bulbs are burnt out, so what is the issue? Is it a transformer or a ballast? I have no idea as I've never had a problem with a fixture before. Any help please?

