If so when you last switched it on did it flicker for 30 seconds and is the lamp black at each end? If very black change starter and lamp, if lamp ends are not black, change starter switch.
Note: Starters for 70w / 75w / 100w are different from "universal 8watt to 65 watt starters. Twin circuit 18w / 20w will need a quality starter.
OK so it still does not work.
Well hi kick may help but causes hernia so .................
Change lamp and starter for ones that are working in another product.
It is possible for a choke ( the box like object inside the fitting) to fail but normally it is because the lamp has been left in a failed condition whilst trying to start the lamp the control gear has overheated.
If it has been left in overheated condition it will have to be replaced by another with a three year warranty from TLC!
What if the fitting is an old 1800mm/ 6 feet long 75/70 watt (or 125watt 2400mm)? Then the lamp may not work because the fitting had a leading circuit with a choke in series with a 440volt capacitor. If stressed by starter switch problems these capacitors can fail after 8 years and will have to be replaced by the same value item.
What if it is a twin and only one side is out? Then if it is a 75 watt the leading circuit capacitor is the problem.
OK so it is a brand new fitting straight out of the box and has never been used.
OK so it is much more modern and has electronic high frequency control gear and it has worked for say two years, personally I would give up and look for replacement control gear. If it has never worked and you have NOT megga tested the fitting then complain!
Suppose it is a new installation and one fitting in ten is not starting properly, have you over loaded the circuit beyond the rating of the switch or beyond the supply current?