Sounds like you may have had all of the win 10 files downloaded to you and when you turned it back on maybe it was trying to install all of the files.
We had to wait a proetty long time time for WIN10 to install the first time aorund... took over three hours as i recall but we always had a gauge screen showing the progress to keep us from turning it off until it finished I guess...
Even doing that we got to a point tha it would not go past so thats when we reinstalled WIN 8.1 after that it all started all over again and finally got past th ponit it failed before and finished up the install. Drink alot of coffee watching my four laptops (WIN 8.1 and WIN 7) get WIN 10 installed on them.
Roy Ken