Had this tab for just under a week, it was on charge this morning, but this afternoon when I looked at the tab. it had a black screen with colored lines down a quarter of it, I couldn't turn it off so just used the reset button and it turned on fine after that, but for some reason it has been turning itself off then on again (there was about 25% charge in battery - not connected to the mains).  and it has done this twice that I have noticed in the past few hours, does anyone know what is going on, or does it need taking back to the shop (if I can as it is flashed with custom firmware - with google play store on it etc lol)

thanks