Definately start with pulling the battery and charging it. If that doesn't do it, try downloading the card to see what (if anything is on it). I'd say a process of elimination is the best bet. You'll have to do something if it's a bad sensor, but you may or may not be able to live with without the LCD. Nikon could, of course, fix whatever's wrong - but it helps to be able to tell them as much as possible so they can help you as much as possible.