I just attempted to install the Windows 10 Anniversary Update and upon reboot the computer seemed to hang on the spinning dots or balls.
After letting it sit for over 8 hours i had to hard power cycle it. Upon restart again the pc started to roll back the changes.
I thought i was in the clear but the next time windows updates ran it did the same thing and hung at the same black screen with spinning dots.
After hours of research I found a tip that worked.
The next time I ran windows updates it hung again at the same screen.
I simply unplugged the wireless mouse receiver and the screen progressed to a Windows screen with the progress percentage.
Not sure it this will work for everyone but ItFixed it for me.