PC won’t boot into windows

Hi, did this suddenly happen? Is there any history that might explain it?

Do you have disk images as we so often urge users to do (e.g. Macrium Reflect (free) ) - or a cloned drive?

Please confirm you can access your BIOS.

Otherwise you'll have to work thru basics.
Please create a live boot disk using Kyhi's iso, available from the top of the Software and Apps section here.

Check your PC boots from it. If you burn it to a DVD- if you have a drive- you will need to change boot priorities in your BIOS.
Otherwise a USB drive- e.g. follow option 2 guide here:
Create Bootable USB Flash Drive to Install Windows 10 | Tutorials

Using that:
Post a screenshot of your partitions using Minitool Partition Wizard.
Test your disk(s) - HD Tune (Health tab and Error Scan)
To post a screenshot please use the Insert Image icon above your post. Thanks.

If those pass, try the Fixboot utility in Macrium Reflect available on that disk.

How difficult would a clean install be?

Example cases (and note what didn't work)
Unable to boot, error codell need to use the - Microsoft Community
Error code 0xc0000001 - Microsoft Community

Note: until it is clear your disk is ok, there's probably little point in suggesting more.

Um, that relies on there being any files in Regback. From 1709 on, there typically aren't, and the scheduled task to create them can't be persuaded to run in 1803, 1809.

I'm not sure the error is in the registry, though...

Yes, many have thought that.. see examples I quoted..

Happened to me once, check the BOOT ORDER in your BIOS! Maybe it's suddenly pointed towards another drive in your PC... (trying to boot off the wrong drive)

Fix the order and you're good to go!