iPad 2 update to iOS 8.4

I am trying to update my old iPad 2 from 7.1.2 to iOS 8.4, I have downloaded the update, and my iPad backed up. But now it is stuck updating, the iPad is now stuck in DFU mode, it gets to "Waiting for iPad" or "Verifying updated iPad software with Apple", and just sits there. I've left it for over 2 hours and it is just stuck. I can't reset it out of DFU mode and it won't update no matter what I try. I have tried 3 different cables.