when the light goes out - and you look closely, can u still see the display?
it can be 1 of 3 problems -
broken graphics card: try plugging your laptop into an external monitor, do you experience the same issue? it is then most likely the graphics card or motherboard
backlight: can you see the display, it is just very faint - as if it's not being lit from behind? then it is most likely your backlight
anything else, and it could be your inverter.
try those two tests - tell me what u find