XPS 2720 won't boot in Windows 10

~1 year old 2720.  It's upgraded to Windows 10, and had worked pretty well flawlessly. 

Last week, there was a boot error, at which point I had the light blue screen with options to continue to Windows 10 (wouldn't work), restart, or take Advanced Options.

In Advanced Options, I ran the hardware tests - everything came out fine.  I then rebooted again - now it just spins endlessly with the dotted circle in the middle of the screen. 

I've done hard shutdowns, and I've gone F12 into the system menus.  At one point, I was able, after about 4 hours of letting it spin, to log in.  And everything worked, but it had to reload all of my music in Groove, and all of my live tiles save 4 or 5 were gone from the start menu.

Once it went to sleep again, I'm back to square one and staring at a blue screen with the endlessly spinning dots.

I'm assuming this is a Windows issue, but I have many machines with the latest updates and none of them have had this problem, and I can't figure it out.

Anybody else seeing anything similar?  Any suggestions on how to fix?