You are posting in the wrong forum ...... this is the site help area.
An admin please move this to general equipment forum.
As to the light - what kind is it, brand, type of bulb - T5, T8, T12, pc
1. If you see a dark band on the bulb, it is likely the bulb is burnt out. A ballast that has the lamps wired in series will not light if one lamp is out. Trying new bulbs is defn the first thing to do.
2. Also check all the connections, esp. the endcaps. Often those are corroded where the bulb pins contacts, cleaning with emery paper might help. Corrosion can happen quickly in damp conditions, eg, when the light is open to water.
3. Unless you have an old fixture with a mechanical ballast, you won't find a starter, so that is not your problem.
4. Before I replace the ballast, check all wiring for loose wires or corroded joints (you would need to disassemble the fixture, and check visually & with an ohm-meter). <UNPLUG FIXTURE FIRST!>
5. Replacing the ballast is a last resort ... that should last 10+ years, so is unlikely to be the problem. However, if you got a cheap fixture with inferior ballast, that might be burnt out. Depending on what bulbs you are driving, you might be able to substitute an electronic ballast from a shoplight (cheapest option, should be under $15). Otherwise you might be able to get something like the Fulham Workhorse form a lighting store (or a parts place like AMRE). You can get the Fulhams over the net for $25 or so ... but then shipping to Canada will cost you. Your most expensive option would be to get a reef tank specific ballast like IceCap, that would set you back $150 or more!