Flourescent lamps can sometimes be a real pain in the butt. I've had some that would only fire off when you held a piece of tin foil between the lamp and the fixture frame.
All I can say is to check that the lamps are turned to their proper position, make sure the connections at the tombstones are good, and try other lamps.
As was stated earlier, T-8s with electronic ballasts are always a good alternative.