Are you saying that the tablet (iPad 3) is the device with the issue? Is the device "activation locked" or did you just forget the pin you use to login? If so, this video might help. https://www.youtube.com/watch?v=QjrpCFLE... Just keep in mind, the devise will be completely erased and reset, but IF you have backups, you should not lose anything. Also, if the device is "activation locked" where it says that the devide is locked to the owner, you can remove the device from your iCloud and shen add it back later IF you have access to it on iCloud. If not, follow this tutorial that might help. https://www.youtube.com/watch?v=VZ0I3GWB...

Did you try to get inside and repair it? If so, make sure everything is connected correctly, something might have gotten knocked and is not seated properly.

Can you tell what the screen says or take a picture and post that here? That would be helpful to find a solution.

Can you try taking a video of the issue from another device and adding that? also, screen recording it from the device with the issue could help to see if it is an issue with the software of the hardware(maybe the screen?)