After a quick google, i found another thread on a forum where someone linked to a firmware. Apparantly after you flash it, it should work again.
ON the download link, one person says it worked another it doesn't. IF you don't mind flashing, i'll send you the link.
BTW. your tab doesn't work and you just take it back from the vendor if you still have warranty? You should have asked for another one, since you didn't unlock bootloader nor did you root.