My house is almost 6 years old and I have a fluorescent light fixture(T12, 2 tubes, 48 inches) in my garage ceiling that recently will not work. I thought maybe the fluorescent lights needed changing and so I replaced them. It worked for a a day or two and now it doesn't work at all. After replacing the old tubes and I first turned the switch on, I could see a small dimmer of light that flicked on at the end of the tube but now it doesn't do it at all. Is it the ballast? the starter? should I replace the whole unit?