iPad Mini stuck in iTunes logo (failed upgrade)
I had the same problem this morning. I tried to update my ipad mini to iOS 8 over the air (without connecting it to my laptop and iTunes), and it got stuck on the apple logo bootup screen.

The workflow described on the following webpage enable me to resolve the situation: http://www.iphonehacks.com/2014/01/fix-stuck-apple-logo-evasi0n7.html

Hope it'll work for you as well!