I'm having this same exact problem too. I've tried to upgrade to 8.1 three times since the first weekend it was released and all three times it has gotten stuck on the HP loading screen. The first time it happened I tried calling HP support, but solved the issue myself before I even got through to someone.
I can't believe this post has been here since October 2013 and HP has not even tried to solve our problem. I really want to upgrade to 8.1 and to continue using HP products, but after this experience my next laptop will be a MacBook.