One PC destroyed, another almost

[faster]

I got hit by the grandmother of all hacks. I can't go into all the gruesome detail, but maybe someone will recognize it and advise me, if I'm lucky. The PC used W7.
First clue was an unauthorized partition, something like "System Security" or something like that. It was given the letter X:/. It came in when I booted my PC, and got the update screen that Windows throws up while it is installing updates. I'd made none, and I knew it was probably foul, but there's NO WAY you can boot up without letting updates finish. That's when I got the partition, I think.
After another day or two, it happened again, over 100 updates, and I discovered that Drive X retained its name but had supplanted C: as the main drive.

Next time I rebooted, the X drive could not load Windows. BYEBYE PC.

More than that, it selectively erased random videos, but erased the entire Musicals folder. Not just on my PC, but also on the memory stick I had bought for the sole purpose of protecting my videos. How it erased them there I can't begin to guess.

I used Recuva and got back a handful of videos, after which I was blocked. Then I switched over to my second standby PC (W10) I had copied many files before I had to really use it much, and the same videos that were erased on the stick and the other PC are also gone.

Now I'm seeing the same signs, and I know my new PC is thoroughly infected, probably with the same hack. I don't dare reboot. It tried to force a reboot, but I had a .txt file which hadn't been saved, and that gave me a chance to cancel. Now I keep a .txt file always unsaved. I disconnect the internet plug every day and turn off the monitor - nothing else. Even with a surge protector, if a storm shuts down the PC, I'm dead meat.

Much else is wrong. It interferes blatantly with downloads, making it impossible to download any security stuff, but when I do, it doesn't work or the file is called "file" instead of "Application" or there are zero bytes in the downloaded file. Stuff like that. Lots of stuff.

This is the only PC expert help site I've been able to use. The others have been corrupted and I can't log in.

Has ANYONE had experience with this? It has destroyed one PC and is on the brink of destroying my other one, after which I'll have NOTHING.

I'd call that serious. The hack seems to be able to know what I am doing and then thwart it, as though they're watching everything I do. It's probably just a program to hack me, but it's extremely sophisticated. Astonishingly deep seated and complex. I don't even dare try to reinstall W10 for fear the "update" screen will block that too. Both PCs were set to boot from the Windows CDs when I realized I was in trouble, but even that isn't enough.

HELP??? Can you refer me to an expert who is at the highest levels of this sort of thing, if this attack isn't known to you?
And if anyone can help me get back into my original PC, I'll nominate them for sainthood. The stuff is all there, just can't access any of it any more.

I just got a popup like happened with the other PC. It says "happiness" is rebooting for your updates. It's 100% foul. I can't reject it. I can postpone it an hour, that's all. Last time this happened, the happiness they delivered was a dead PC.
PLEASE! it is truly urgent. If we have a storm tonight and get a power outage longer than my surge protector lasts, I'm dead meat.

This is a very unusual problem. I don't expect you have experts on hand with this deep sophistication. If you can't help me, okay, but please tell me who might.

How many people can afford to lose two computers?