This is caused by incompatible power flex cable. you will notice this when you see the smart cover function not working after you install a new flex cable. If you notice so then you will not be able to reset the device and add another iTunes account as when you reset iPad and while setting up as new the iPad will not recognize the smart cover function and the worst part is the smart cover function will be turned on deactivating the power switch sleep function. If you happened to see the smart cover function not working then make sure to keep a backup of iPad so that you can restore when needed. The other option is to replace the flex cable with smart cover function which is kind of hard to find.