1. Use a Windows 10 installation DVD to reliably boot into a recovery console.
2. Select recovery mode.
3. Launch Command Prompt.
4. Enter diskpart
5. Run list disk and note the desired disk number.
6. Run select disk <number> choosing the desired disk.
7. Run list volume noting the volume that is about 100 MB, FAT32 formatted. This is the EFI volume.
8. Run select volume <number> choosing the EFI volume.
9. Run assign letter=b:
10. exit from the diskpart utility.
11. Run cd /d b:\EFI\Microsoft\Boot
12. Run bootrec /fixboot
13. Run ren BCD BCD.bak to backup the corrupt bootloader configuration, for some reason.
14. Run bcdboot c:\Windows /l en-US /s b: /f ALL
15. exit from Command Prompt.
16. Remove the Windows installation DVD.
17. Reboot.
18. Optionally, correct the BIOS UEFI boot order, experimenting with different Windows boot priorities until you find the right one.
19. Hopefully, Windows boots normally once again!