Why does this keep going to the "battery charging" screen?

The warrenty has long expired on this old tablet, but I was still trying to figure out how to get it to work again. I’ve tried resetting and restarting, and it can get to the home screen with the basic water droplet background. I can tap on settings and go into it. I can look around for a minute or two to try and figure out the problem. But it keeps turning off and going dark. Then it lights up, showing the Nextbook logo, then the empty battery screen. Then it goes dark again. And comes back on with the “charging” battery screen. I’ve tried a firmware update, and it says there’s no firmware update needed. Most curious of all, the square (recent apps) button, and the circle (home) buttons simply show up the oval around them to say, “Yeah, you touched it.” But they do absolutely nothing. However the triangle (back) button still works fine. Any help?

Edit: Also, is there any way to completely factory reset it? I wasn’t allowed to go to the app store until I signed in with a “Google account associated with the original owner,” or whatever. Basically it asked me to sign in with one of the accounts I HAD signed in before on the device. Is there a way to reset ALL memory? I’m not worried about losing anything on the device, it’s empty anyway. I just want the thing to work, and to start over fresh with it, as if I just got it out of the box.

Edit 2: The menu you pull down from the top is also choosing not to work at random, if that can be fixed also, I would be very grateful.