After upgrading to iOS9, iPad2 stuck on 'slide to upgrade'?

Once I am done with sliding, it will ask me for the ipad password, then an Apple logo will show up with an update status bar underneath. Each time the status stops at the 1/5 location, and after a few seconds, the same white screen with "slide to upgrade" on the bottom will show up. The same procedure will go forever. If I connect the device to iTune on my desktop (as many have suggested, including Apple Tech bulletin board), I will be asked by iTune to hit 'ok' on iPad, but because iPad is stuck, the 'ok' panel never shows up. Because of that iTune never displays the device.

Help! I am urgently needing to get something out of my IPad -- medical prescription, Help will deeply be appreciated.

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