there are a couple things I'd check with fluorescent Lights:
One I'd pull the buld out and open the light up by taking the cover that hides the wire connections off. I'd check and make sure the connections are tight, but pay attention to the ground. make sure it's tight. Without a good group the flor. won't work properly.
two: make sure you are screwing the bulb in tight. sometimes a flor. bulb seems like it is locked in place and it is not. make sure both of the prongs on each end of the bulb are in the holder and twist til you feel it lock in.
three: make sure the little wires going in to you buld holders are pushed in good. and make sure the bulb holders are pushed in tight and not being pushed away from making the bulb get a nice tight connection.
hope these few sugestions help