On your PC, install Recuva. Connect the tablet to the PC and enable USB storage. Windows will assign a drive letter to both internal and external storage. Open Recuva, select the internal storage, and let it find your missing files. Select all the files and then select a location on your PC's hard drive. Let Recuva retrieve your files.
When Recuva finishes retrieving what files it can, head to Amazon and purchase a new tablet. Your tablet has a hardware issue, and if I were to guess, the constant heating of the motherboard from the processor has caused the internal storage chips to pull away from the motherboard, breaking the connection.
If Recuva cannot recover your files, there is nothing that can be done except purchase a new tablet.