Locked out even as administrator

I fired up an infrequently used PC (Lenovo ThinkCentre M53) only to find that I am locked out of several functions such as device manager. A red banner comes up that says:
This app has been blocked for your protection
An administrator has blocked you from running this app. For more information contact the admistrator.

mmc.exe

Publisher: Unknown
File origin: Hard drive on this computer
Program location: "C:\WINDOWS\system32\mmc.exe" C:
\WINDOWS\system32\devmgmt.msc

I can run device manager from Admin version of Windows Powershell

Windows version number is 1903. All my other Win 10 PC's are 2004
Also Windows Update says that I am up to date.

Thank you. John

Version 1903 reached end of service life earlier this month.Unless it has data you need,why not lnstall the latest version?

Thank you for your reply.

Is a total reinstall of Win 10 the only way to fix the problem? Yes, everything is backed up on a commercial offsite backup service, but reinstalling programs, etc., would take hours.

How about a real fix for the problem? Obviously something is wrong. SSD checks out fine ccleaner did not find problems with bad registry values.

How can I force Windows Update to update?

smoketoxdoc said:

...device manager. A red banner comes up that says:
This app has been blocked for your protection
An administrator has blocked you from running this app. For more information contact the admistrator.

mmc.exe

Publisher: Unknown
File origin: Hard drive on this computer
Program location: "C:\WINDOWS\system32\mmc.exe" C:
\WINDOWS\system32\devmgmt.msc

There is something very wrong there. For a start, the 'Publisher: Unknown' for mmc.exe is unexpected. If you have UAC turned up to maximum you'd get this on trying to open Device Manager...



...which clearly shows that the publisher is known, and it's Microsoft. I'd run SFC /ScanNow from a Command Prompt (Admin) to find and fix possible corruption. And if it finds corruption it can't fix, follow that with DISM's RestoreHealth option, then run SFC again.

Run SFC Command in Windows 10

Use DISM to Repair Windows 10 Image

If that fails, then an in-place repair upgrade should fix it, and allows you to keep installed files and apps.

Repair Install Windows 10 with an In-place Upgrade

Thank you very much for your suggestion. I had forgotten about scannow, etc. Not the first time I have had to use it with that particular PC. SSD is Scandisk, not Intel.

Scannow found errors. Ran DISM, and it went to completion, but apparently did not fix problem.

John

Are you logged into the built-in administrator account?

Thank you Navy LCDR. No, I am not logged into the built-in administrator's account. In the time I have had this particular PC as well as a half-dozen others I have with Win 10, it has not been necessary. Would it help in this particular case?

John