Ok i just had the same problem about 30 minutes ago with a cracked digitizer and had to replace it on the ipad 2. After the replacement i closed everything back up and realized the backlight wasnt working when it was before i did the replacement. so i had to open it back up and reseat everything this did not solve my problem.
LET ME NO IF THIS WORKS I HAD TO RESET THE IPAD BY HOLDING THE STANDBY BUTTON AND HOLDING THE DIGITIZER UP TO THE LCD AND TURNED IT OFF THEN ON AGAIN IT WAS THAT SIMPLE FOR ME IDK WHY I DIDNT DO THAT IN THE BEGINNING IT MAY NOT BE THE SAME FOR YOU BUT LET ME NO.