My Ipad 3 Wifi did the same thing. I had no screen, but if I "shorted" the home button contacts, I heard sound so I knew the system was functioning. I went ahead and removed the logic board and disconnected it from the battery (after disconnecting the top power switch ribbon assembly from it) and left it disconnected from the battery contacts for 30min. Put it back in and reconnected my button harnesses and tada! Screen was back on with my Apple logo.