The answer to 'my lighting installation won't turn on' is that there could be several common causes, including a tripped circuit breaker, a faulty light switch or fixture, or a problem with the wiring. Symptoms may include the lights not turning on at all, flickering, or only partially working.
First, check your circuit breakers to see if one has tripped. If so, reset it and see if that solves the issue. If the breaker keeps tripping, there may be an electrical short or overload that needs to be addressed by a professional electrician.
Next, inspect the light switch and fixture. Make sure the switch is in the 'on' position and the bulbs are not burned out. If the switch or fixture appears damaged, you may need to replace them. For more complex wiring problems, it's best to call an electrician, as improper DIY work can be dangerous.