On my Dell 2-in-1 (laptop/tablet), I ran the Windows 10 Creators upgrade. It proceeded normally, doing several restarts and presenting me with a display of the new features. However, the computer was running very slowly, so I did another restart. It hung on the circling dots stage. I turned it off and on again, and again it hung on the circling dots stage. I left it overnight -- still hung on the circling dots stage in the morning. I turned it off again, and tried to turn it on, but it did not turn on (though the under-keyboard lit up, so it has power).
Of course, this problem may have nothing to do with the upgrade. Any ideas?