Small UAC problem.

Alan,

[this is the second of my two recent posts and they might be separated by a page break so do look at the bottom of page 1 if necessary to see the first post]

That first diagram [the one that shows the orange title bar on your command prompt window] worries me.
- In that diagram, I can see that you were in fact attempting to alter a property of the user account that is called "Administrator" - that is what that line containing ... where name="Administrator" ... actually means. That is not your Admin account, it is the user name of the Built-In Admin and you really ought not to alter any of its properties. You were saved on that occasion because you did not have the authority for the command you were trying to run [so nothing was changed].
- That diagram does not show the full response to your net localgroup administrators command - the photo does not show anything after the Members line and it is the data after that line that matters. You have already said that NewAdminPrimary is your only Admin account so I would expect only that and Administrator to be listed below that line. If you had also created another Admin account then it would also be listed & it could be used to rescue the situation.

Denis

Alan,

Just to verify, did you boot from a Windows 10 installation USB when trying to open a command prompt at boot?

Enable or Disable Elevated Administrator account in Windows 10 | Windows 10 Tutorials

Alan,

1 If, whilst logged in using the Standard user account called Alan, you cannot open an elevated command prompt / elevated Powershell window then 'normal' procedures will not be possible. You have not said what happens if you try.
2 You will need to use the procedure in the tutorial about enabling the Built-In Admin in order to create an additional Admin account in order to sort this out - Enable ... Built-in Elevated Administrator Account

Main rectification actions -

1. When you enable the Built-in Admin & log in with it, you should create TWO password-protected Admin user accounts.
2. Assume that your existing Admin user account, NewAdminPrimary, is a writeoff.
3. Call them something like AdminPrimary, AdminReserve.
4. Write their passwords down somewhere secure yet readily accessible to you [as I probably said before, mine are on a strip of paper inside one of those dog name tally holders that I have attached to my keyring].
5. Log in to Alan again.
6. Open an elevated command prompt / PowerShell window to test the AdminPrimary username & password.
7. Open an elevated command prompt / PowerShell window to test the AdminReserve username & password.
8. Then disable the Built-in Admin again.
9. There is no particular benefit from logging into AdminPrimary until you need to do so but it will do no harm.
10. You need not bother logging in to AdminReserve either but it will do no harm.

Essential follow-up checks -
Open any command prompt / PowerShell window and enter

net user Alan
then net user AdminPrimary
then net user AdminReserve
then do it for that faulty account net user NewAdminPrimary

In the response for each test, look at the line beginning Password expires and, if it says Never, be glad. If it has an expiry date then use the link @Brink gave you to change it to never - Enable or Disable Password Expiration for Local Accounts in Windows 10 | Windows 10 Tutorials

That should be it. Post back with progress & any problems.

Best of luck,
Denis

Alan,

If you like, you can create the USB on another computer (friends if needed) and boot from it on your computer.

Create Bootable USB Flash Drive to Install Windows 10 | Windows 10 Tutorials

Alan,

You don't want to start the installation.

Instead, you would only want to boot from the USB, and do Option Five below to enable your built-in Administrator account.

Enable or Disable Elevated Administrator account in Windows 10 | Windows 10 Tutorials