You most likely have a bad tablet :/ Contact your seller and see what options the will offer you. I have a chuwi whos sd reader died, connecting the sd card via usb works for me untill this gets resolved.
i posted my solution here http://techtablets.com/forum/topic/some-problems-with-sd-card-reader/http://techtablets.com/forum/topic/some-problems-with-sd-card-reader/