Same thing happened to me. Had to force it to turn off . Went to the Apple store to get a techie to plug into their computer and it was recognised. They said it needed to be turned off for a while Had to do a full restore. iPad had same problem and had to restore it to a new iPad as it kept crashing when I tried to restore computer backup.
I am having trouble now with my email downloads.
Definitely not worth upgrade.
I messed around with it for a while with no luck so I went to my local ATT store and dealt with my gal that has been helping me since the mid 90s. She plugged it into her PC and luckily it showed up on her iTunes so we did a full restore on her PC. Once the full restore was complete we plugged into my PC and my iTunes finally acknowledged it. So I chose the option to restore from prior backup (the one that I did right before I attemped the iOS update). It went thru and did the restore from backup like it was supposed to but when it rebooted it wanted to set the phone up again. I tried the restore from back up two more times, but the same outcome. So finally I told it to just set up as a new phone and it finally let me get all the way into iTunes. Unfortunately I then had to redo all the foldering and everything on my phone, but luckily I did not lose anything to my knowledge.
I have yet to update my iPad 2. Time will tell if I will have to go thru everything again.