I have a little different issue than yours after replacing the touch screen for my IPad Mini. The power was off, but I did not remove the battery connector before unplug the screen and the LCD connectors (I knew that it was a bad mistake). After replacing the screen and put everything back together, I can see the back light came on with an apple logo. However, the back light went off after booting, and I can see the password screen. I took a flash light and shine behind the LCD for entering the password to see the screen working. The screen worked well at all corners, except the back light. I powered it off with a flash light behind the LCD, and I powered it back again. The same thing happened. The apple logo appeared with back light during the booting time and turned off after that. It was working fine before replacing the screen. I did a backup with iTunes without any problem, but the back light is still turn off after booting. Do you have any idea? Thanks in advanced.