Is the reboot slow because it's doing the 5GB download of Windows 10 ?

Edit:- As per pipexer's reply to this post, I too missed that the OP waited 2 hours. What follows is therefore not relevant to the problem, but may be useful for some readers.
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I find Windows startup screens when completing an update can also go blank/near black for many tens of seconds even on recent Intel i7 chips with 16GB of RAM and pure SSD disc.

I wonder how long the OP has waited before believing it has hung? I have gone a way for minutes before now and come back to find it saying it is processing update 1 of n.

Edited by RobertoS (Mon 19-Oct-15 00:01:05)

You're very right about that, funnily enough I've described it the same way to people i.e., even with i7 and SSD you can get a few seconds delay.

In the OP though (I almost missed it myself) he did say he waited 2 hrs so that should be plenty

So he did. Oops!

Does it do a restart Ok, if not installing updates?
Have you tried using msconfig to do a clean boot with out any startup programs, apps or 3rd party services.
Have you tried using/creating another user account or enabling the admin account?