Q: Update issue - Please Help!!!

I'm in the middle of updating my I Phone 4, It asked me to allow access to my PC which I agreed to, it's now asking me to respond on my phone to confirm but nothing happening on phone? I've tried unplugging it from the PC and back in again but doesn't make any difference. The Screen is currently showing Apple logo and a half full bar underneath, and won't let me turn it off. Any ideas on how to get it moving again - it's driving me crazy!