I have always struggled with fluorescent lamps over the years. It seems like the y just stop working, then start up again. Sometimes I'll swap in new bulbs to no effect. Bulbs I thought were dead work in another fixture. Lamps flicker sometimes, etc.
After stumling across this site:
http://members.misty.com/don/f-lamp.html#int0
... I may know what is going on. Apparently, on rapid start fixtures (like most of us have) grounding the lamp chassis is important. Not just for safety reasons but for starting reasons!.
Apparently the capacitance between the bulb and the refelctor assists in starting!
I recently obtained some used 4 bulb 2x4' fixtures, and I did the normal frustrating dance of bulb swapping with inconsistant results, trying to find a combination that works. I wire nutted a simple lamp cord with no ground onto the thing and was trying to get it to work with poor results.
After reading the article, I swapped in a grounded cord and shazam! It started working!