I bought a Win 10 Pro Dell-PC i7, never connect it to internet(Used for photo editing) until recently. IT was on 1511.
When connected to INternet it forcefully just updates & updates, and kept on.......
I waisted two days of bandwith with zero results. It got stuck at the update before 1706....just eating bandwith with no end in sight.
Maybe you can try this:
I then downloaded Microsoft Windows 10 update assistant, let it run and fixed problems.
I then use Win 10 troubleshooter itself for updating, on which it fixed a few problems.
The result was that it skipped the intermediate updates and went straight to 1706 without any problems then. It downloaded half a day, and install correctly, no ISO or any of that.
It worked perfectly till recently(2017-09-14) KB4038806, KB4038788 was installed, then the Win 10 Apps i dont use started to fail(Event viewer notes).
It still works well, except those Apps not opening.(Dont need them in any case).
I am now waiting for the next big update in Oct 2017 to hopefully fix those.