I was trying to change for the second time my ipad4s digitizer and I forgot to shutdown it before process... so after proper installation backlight problrm hit me! I closed room's light and put light on screen and saw nothing! But emprically-when charging from computer- tried to shut down on the black screen and I succeeded.. waited for ten minutes and when I open the pad it was on!!! But with a nonfunctional homebutton.. thats a success for now :)