Hello all,
I want to take a moment to repeat what one of our engineers posted in a separate post that should be of some help:
For customers experiencing difficulty updating their systems to Windows 8.1 Update, I want to let you know that we are working to resolve as quickly as we can. Many customers have been helped by following the steps suggested in the beginning of this thread. If following the troubleshooting steps listed in this link does not help, we ask that you contact Customer Support directly by clicking here as this is the only way for us to assess your individual situation.
Thank you for your understanding.