When I went to turn off the computer it automatically went into an upgrade which it did quickly. When I next turned on the tablet a day later, I can only get a blue screen that says it is still upgrading, has reached 100% of upgrade and do not turn off the computer. It has now been like this for over 24 hours and I cannot get the screen or the computer to turn off? What can I do to get my tablet to work again? Thanks for your help.