Any helpful experience to relate?
Sorry..... No, no personal experience as I've never had this happen although I've seen multiple posts on this forum and other regarding what sounds like the same or similar issue.
I suspect that the problem is linked to corruption with the Microsoft "Spotlight" App and probably not a $200 virus.
As "Spotlight" is not commonly evoked in a Safe Mode boot, my first suggestion would be to attempt booting the system into "Safe Mode"
You can boot the system from the installation media and use the Repair Your Computer link on the second page to get you to Troubleshooting -> Advanced Troubleshooting -> Startup Settings
To restart your computer and then select #4 (Safe Mode) from the available options.
If you do not have the installation media on hand you can use the media creation tool and download the ISO from here
Once you have the ISO, you can use ImgBurn to burn it to a DVD, http://imgburn.com/
or Rufus to burn it to a USB ThumbDrive, http://rufus.akeo.ie/
either of which you can use to boot your computer.
You might also try forcing the machine to boot to the Windows Recovery Environment by.....
Using the power button on the computer to halt the boot process three times..... usually the third time will produce the Recovery Environment and allow you the same steps Troubleshoot -> Advanced Troubleshooting -> Startup Settings
Just start the machine with the power button and when you see the Windows 10 logo, usually accompanied with a circle of spinning dots, press and hold the power button until it shuts down completely no lights, no fan or drive noise.
After choosing #4 from the "Startup Settings" options you should see your user name with a password box.
IF you can then get to settings, change your lock screen from "Spotlight" to a static picture. Just choose one of the available options for a picture from the three or four presented.
Reboot the system normally and see if that helps.
IF for some reason you can't get to Settings -> Personalization -> Lock Screen ….
Then you've got some reading to do on alternate methods of …..
Resetting and re-registering "Spotlight".