I actually created a Microsoft account to vent on this thread. I have had the EXACT issues. Windows 1703 will NOT install on my desktop and I've tried for MONTHS. Then suddenly the past week my computer has been hijacked by this update assistant that stalls everything I do on my computer to force me to install the 1703 version even though it ALWAYS stalls at 81 percent.
In the past 48 hours I have trues several fixes, including reseting my computer twice and wiped out all personal files (after I made copies, of course) and the dreaded 1703 version still WONT load. I am incredibly disheartened to read this thread and not see a fix I haven't tried.
I fear I am going to have to do one or two drastic things. Completely unplug from the internet to stop this update assistant from hijacking my computer and frustrating me while I work and just use my phone to check email ... OR buy a new computer. So I'm forced to either have a glorified typewriter or shell out hundreds of dollars I don't have because Microsoft has put a virus-like program on my computer. By the way, if I have to get a new computer because of this issue, it will be an Apple. This experience has been horrible and has wasted HOURS of my time.