I fixed the screen on my tablet, but noticed that the display was also damaged. So now I have to find a replacement for...

It might have to do with the battery being the issue. It could be that the battery is not working right, or for some reason the connection between battery and motherboard is disconnected. If the battery is disconnected, then that is easy to fix yourself. Just remove the back of the tablet to see if the battery is connected all the way.