I had a similar problem after installing windows 8 on a laptop. Windows update appeared to hang with nothing happening but updates were being downloaded.I suspect your machine seems to stick at the "restarting" screen because updates are being installed although there is no indication of this. I suggest that you start windows updates and just leave the machine for an hour or so to see if things resolve themselves. That is what happened in my case and Windows Updates now works perfectly.
HTC U12 Plus review: Hands-on