some florcents have starters that will over time go out. you can usually find replacements pretty cheap. I think Petco has them for like 5 bucks. they are small cylinders that plug and twist in near the bulb or into or near the ballast of the fixture. If your fixture does not have either. The it is possible the balast of the fixture has simply gone out. in most cases you can opt to get a retrofit kit for it and just rip out the enternals and wire in the new better bulbs. or you can just replace the whole thing.