does it have an accessible starter.? ..some old fixtures had a cylindrical shaped starter located just under the light tube on the fixture.
Also try removing tube, reverse it and then reinstall it. Press on off switch once you install it to be sure it is "on".
Do you have another tube from another light in the house to test if it's the tube? How old is the fixture.
You could also try bypassing the switch by opening up the fixture, cut the wires ( make sure you unplug unit first) going to the switch and then strip the ends of the wires and twist them together and then use electrical tape to cover the joint.
Also try removing tube, reverse it and then reinstall it. Press on off switch once you install it to be sure it is "on".
Do you have another tube from another light in the house to test if it's the tube? How old is the fixture.
You could also try bypassing the switch by opening up the fixture, cut the wires ( make sure you unplug unit first) going to the switch and then strip the ends of the wires and twist them together and then use electrical tape to cover the joint.