there are 2 possible reoasons for that problem - a defective inverter or faulty ccfl tubes. is the backlight complete gone ? (sounds like it)
i would guess it's the inverter
changing the part is easy on this model, use the [guide|979|inverter replacement guide]
depending on your exact model, the inverter is in the ifixit store. i don't know where are you from and sometimes the shipping could took ages (or is extremely pricey) - maybe you have a local shop or an ebay seller in your area/country who is able to deliver the part faster/cheaper (not that i won't support ifixit - but sometimes it simply makes no sense to order "there" - if i would need this part, it would cost 99$, i need it fast, that makes ~35$ shipping, german taxes and customs are around 28% - that would make 171,52$ for a part that i can get here in my area (germany) for around 60$