Not all LCD's are a-like!
You see LCD technology does not itself emit light. you either must have enough ambiant light to see, or it must be 'back-lit'. The Technology formmerly used to do this was CCFL or Cold Cathode Forescent Lamp, these failed in 2 different ways as they aged.
1. the light would get darker as it aged. Some would even change color therby messing-up the colors the display rendered.
and
2. As the bulb ages, it requires more and more power to engergize it. Eventually it will reach a point where the amperage required to start the lamp, will exceed the capacity the circut it is on can provide and simply not light.
If you've ever seen this, or suspect that this is your problem (display won't light, or goes dark shortly after starting,) simply shine a bright light source directly into the display, you should see faintly whatever the desktop was diplaying at the time.....or your desktop if it never came on to begin with.
Current Backlight technology uses white LED lights....far better.
the BEST ones use 3 LED lights....1 each of Red Blue and Green, much much better at displaying the full color spectrum.