Summary:
My problems arose in Windows from updating Windows 10 to the 1803 version. You get a blank screen and the Recycle Bin, the only icon that's really working. You can get at task manager (CTRL-ALT-DEL).
There's a good description of the problem here, but I did not try the solution proposed at this link:
https://www.surfacetablethelp.com/2018/05/unavailable-desktop-with-recycle-bin-on-black-screen-on-windows-10-v1803-update.html (https://www.surfacetablethelp.com/20...-black-screen-on-windows-10-v1803-update.html)
I tried to use task manager to get at things, and fortunately had a full, recent backup of the C: drive on AOMEI.
Nevertheless, it's not possible with the backup I had to create a bootable drive. So, while I didn't lose a single file, I ended up performing a clean install of W10 and what I DID lose was v5.7.3 of Kontakt, which "broke" a few other things.
EvilDragon suggested I substitute the EXE and DLL files from my old drive into the now-new Kontakt 5.8.1 that downloaded from Native Access. That helped, but unfortunately I lost the ability to "add library" directly from within Kontakt.
As you may know, v5.8.1 allows one to add a library only from within Native Access, and I'm unable to add EWQLSO Percussion XP for some reason -- everything appears to be in place but it won't add in. This despite the fact that the old "regular" EWQLSO Percussion does work. The XP patches appear as DEMO and time out quite quickly, so if I can't figure out how to add them back, I won't be able to use them anymore.
As I said, I am able to load patches from the even older Kontakt version of the EWQLSO Percussion library (the one without extended content). Just not the expansion.
Everything is now back in order except for:
1. Can't open very old East West (Kontakt version) of Percussion XP, which is too bad, because it has a Wagner bass drum and a few other very good sounds on it. I'll call Native Instruments today and / or put in a ticket.
2. I had an install from long ago -- can't even remember how long ago -- of Abbey Road 60s drums that had about 20 or so kits. Native Instruments made me "Install" the library and now there's an entirely new library with the same name that only has four kits (two really, since it's just the "full" and "lite" version for each of two kits).
So now, on the good side, I have a fresh, clean Windows 10 install and didn't lose too much.
On the bad side, it has taken nearly a week of tinkering to resurrect the PC the way it was. I have a complex setup, with I don't know how many libraries, plus a software RAID on one of the drives (which didn't help).
The other bad thing was that I reset my BIOS to its default state and I'll have to go back through that to turn off Speedstep and some of the other "helpful" power management items. Also, of course, one has to go through the "Settings" in Windows 10 have to have all the non-music rubbish (background tasks and microphone access and all that) turned off.
And I disabled "Windows Update" in Services. I won't be using that any time soon!
John