Your Kindle shut down? If so you should see the boy under a tree and the update bar going across the screen. Oh, wait, you did put this in the Fire thread, so perhaps you mean a Fire? Make sure it's completely charged and then do the 40 second reboot method - it won't work if there's not enough battery power.
is it possible (I've seen this reported a few times) that you accidentally turned the illumination all the way down? People have fixed that by going into a completely dark place where they can "barely see" the illumination controls, and turning it back up.