I had the same problem but I was fiddling with my 3ds today and I found that if I held down the Power Button for about 10 seconds, it turned on again. My situation was that I went out, decided to place it in my bag for a while. However, when I reached home, I found that the 3ds screens were black but the blue light and the other orange light was on. When I charged it, the charging light comes on too. So I figured that maybe I put it in sleep for too long or something.