In this case try to flash stock firmware by Flashtool. Start Flashtool, select scatter from stock firmware folder, push download, then connect pad to pc. After it press volume up+power on for long time. After some time pc catch the pad and firmware would be start flashing. If not, try to reinstall drivers from alldocube website. After flashing, disconnect pad from pc and hold power button to turn it on. Beware, all users data from pad will be lost.