why do i have no LED anywhere on my screen or keyboard?

I have a macbook air 13" that has no LED backlighting on screen, apple logo or keyboard. Possible fuse? Person I received this computer from said they thought it was the display but I would believe it to be a fuse or firmware issue? Any opinions or ideas? (I'm not an extremely experienced in computer electronics but have a great diagnostic skills in mechanical and automotive electronics, so, I will get the idea pretty easily.) Scott