Predownload complete, now what?

Ive had a 6.66gb $Windows.~BT folder for 6 hours, not sure whether i should press setup?

whats preventing my system from going ahead and upgrading??

Even if you click setup.exe it will give you an error and it won't install.
I have another computer running on 8.1. It has finished the download too but still waiting. Microsoft is distributing this update "in waves", I think that's why some computers still haven't got the update.