| Assuming that you HAVE tried re-seating the tubes to make sure that they are indeed properly seated, that sounds like a bad ballast.
Unless you are reasonably comfortable messing with electrical wiring, it's best to get an electrician to change the ballast. However, it's not really that difficult if you follow the instructions one step at a time.
1) Purchase a new ballast for that type of fixture
2) Arrange for good lighting up where the fixture is.
3) Test that lighting and make sure it stays lit when you turn the bad fixture off.
4) Arrange for a ladder or a table to stand on to comfortably reach the fixture.
5) Arrange for a helper to steady the ladder and to pass pieces to
6) Turn the bad fixture off and remove the tubes.
7) Unscrew the metal safety cover and remove it.
8) Draw a diagram of the wiring that you see.
9) Make sure that the ballast is an exact replacement with the same numbers and colors of wires.
10) Loosen the screw or wing-nut that holds the ballast and just let it hang by the wires.
11) Attach the new ballast securely
12) One at a time, switch the wires from the old to the new ballast
13) Double-check the wiring with your diagram
14) Make sure the little hat type connectors are good and tight and that you can't pull them off.
15) Replace the safety cover
16) Install the tubes and plexi-glass cover
That should do the trick.
Have FUN!
DearWebby
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