My Android tablet seems to be "read-only"
I am facing the same issue with my VOX V81 tablet. I formatted its internal storage and did a factory reset. But when I rebooted it, it came to its previous state.

I suppose that it is due to the Avast Mobile security I installed on this tablet; after installing Avast, this problem started. So I suggest you to uninstall any antivirus or mobile security application.