Win10 logon

"The account could be unlocked by Microsoft which I discovered through Safe Mode."
What exactly does this mean?
If you mean that the Built-in Admin was shown as a sign-in option in the Safe mode login screen even before you had enabled the Built-in Admin yourself, that it highly significant.
- It means you have no other functioning Admin accounts on the computer.
- So use the Built-in Admin to create two local, password-protected Admin accounts of your own.
- Log in to each one to test they work correctly. If you get that incorrect username and password message with them it means your hidden C:\Users\Default is corrupt.

"that was first thing without result"
I do not know what you are trying to say.

I have no idea why you are referring to, I suppose, a Repair install procedure or Bitlocker.

wasislos said:

If I reinstall will that user go away or will I be stuck?

No, a Clean install recreates a new user account from scratch.
But don't you have a system image to fall back on? That would be quicker.


All the best,
Denis

Then rescue the user files first, those that have been updated since the last backup.
Boot from an InstallUSB or Macrium reflect boot USB and use its command prompt.
Use InstallUSB Notepad as a rudimentary File explorer to backup files [post #33] - TenForums
I've gone a bit further with my InstallUSB, I've added a portable Explorer++ to mine. Much more convenient than pressing Notepad into service.

There is nothing called Repair mode. I assume you mean a Repair install procedure.

I do not know why you think Safe mode would help you.
F8 is not a method of getting into Windows 10 Safe mode. You're thinking of Windows 7 & earlier.
Boot into Safe Mode - TenForumsTutorials

There is a suggested [yet disputed] fix for a failure to create new user accounts correctly but the fault's symptoms were not the same as yours. Those symptoms were a The User Profile Service failed the sign-in message and the fix was disputed at the time I saw it discussed [about six years ago, I didn't keep any notes].
- Boot from the InstallUSB / MR boot disk and copy in the entire C:\Users\Default folder from a computer that does not have the login problem.
- Personally, I'd rescue any non-backed up user files and then give the Default thing a whirl afterwards.

Try3 said:

But don't you have a system image to fall back on?

Best of luck,
Denis