I was going to suggest the volume + power button to bring up the hidden menu if android but as you say it doesn't have one.. I used to deal in tablets, china tablets, I would suggest contacting the manufacturer and asking them for the firmware so you can restore the tablet. Back when I was selling them the factories I got them from sent me the firmware for the tablets and one of their chinese programs I had to use to restore the tabs that had problems, might be worth contacting them :)