This is what i did to solve the same problem with the backlight: Powering down the iPad before repair is good but you still have the issue. When you remove the digitizer screen, do NOT unplug the LCD unless it needs replacing also. If LCD is needed, unplug the battery FIRST (the cable that runs between the batteries) then unplug the LCD and replace. Before laying the LCD down where is goes, plug back in the battery and you should see the LCD light up through the holes in the back of the LCD. Hope that helps and remember to go in that exact order.
Bobby
Texarkana Tablet Repair