Some thoughts...
How long did you wait before powering it off?
Have you tried reseating the eDP cables? I had this issue when I installed my AMD mainboard, but it showed up in the diagnostic lights (11 green, 1 red) so I knew what to look for.
Do you see anything on the display if you shine a bright light on it? If you see stuff when you shine a light then it's most likely a backlight fuse.