I was reparing my ipad 3 cu's the screen was shattered but the lcd fine.
I didn't realize that the battery was empty. Whet I was starting to test the screen the lcd didn't turn on and starts beeping, I thought I was screw that I broke something.
In my desperation while the charging cable was in and ready for charge I heard the beep so press simultaniously the power button and the home button and it stopped beeping and suddenly the apple turn on and when it finally finish turning on I see the battery and it was 1% and I charge it and problem solve. I hope this helps anyone out there =)