Maybe you done something wrong, open up again and check if cables are well distributed and not wrecked anything, my tablet was like this, led was fine, tho for a little wreck in the cable when I tried to close and did it wrong, it screwed it up. (also with a phone I had, which doesn't turn on anymore when I tried to fix this same issue, on it).
You must be very careful and check twice if everything is fine. Tho as I said, if bootabimation and charger mode are normal, must be something on system.
Enviado de meu LG-E975 usando Tapatalk