LOL, Goddamn Windows 10.
Brand new rig. Nearly $4k down without even the monitor, brand new shiny install of Windows 10. Boot it up, manage to get the initial screen and give it the new key. Update all the various privacy settings that every recommends (holy poop there are a ton that Windows tries to set by default).
Figure I'll give it a nice new reboot . . . and now it's stuck in an endless Diagnostic and Autorepair loop. I have literally not installed or been able to do anything else yet.
To be fair, I shouldn't be surprised . . . but come on!