I hope this helps. First check how much available storage you have right now. If you see that your under 1GB then try to delete apps that you don’t use as much. Make sure that you close your background apps as well, thus making sure the brightness is not too bright unless needed so. Make sure your device is up to date on OS updates . If nothing of this is working. Then backup all of data on your laptop or iCloud (i usually back it up on both just to be safe) and confirm your data is back up, then perform a Factory Reset, on Settings - General -Reset or on the computer. I personally prefer doing it on a computer but you can pick your preference. If nothing works, then something could be wrong with your device, getting a replacement would be the choice if possible.

Replace your phone speaker

Yes Try Factory Reset. If it doesn't work then probably its going to be hardware problem, which i hope is not. But try erasing it via iTunes.

If restarting your phone didn't work then Back Up your phone with iTunes or iCloud. Fully erase your phone using iTunes via Computer. Then restore your backup and hopefully that can fix the problem.

Probably your battery has a small hole . But I recommend to change your battery.

My opinion seems like the LCD needs to be replaced.

Alright, well to be safe just don't charge your tablet. Second, you need to get your tablet checked out. Probably there's a lose cable, as in the connection. Pretty sure it has to be one of the three that could be the issue to your problem the , battery, LCD, charging port.

If you have a disc or a USB with Windows 8, then re-image your OS, unless you don't have any important documents. Or unless if your laptop boots up normally loading the OS, refresh your system, which is going to give you the follow options, for what you want to keep and delete.

Have you tried charging it ? Have you overcharged your device? How long did you had the device?

You can try un- installing the app and re- install it.