my iphone 6 has had no progress restoring an update from itunes in 3 hours

My iPhone 6 was stuck in a restarting loop so I was suggested to restore the phone from iTunes. I followed the directions on support.apple.com/iphone/restore and began the update. iTunes has gotten to the point of "Verifying updated iPhone software" but no progress has occurred in 3 hours. My phone is stuck on a screen with an empty loading bar. iTunes also no longer shows the serial number of my phone. What went wrong? What can I do now?