a) Press Windows and x key together on your desktop screen.
b) Click on Command Prompt (admin).
c) Type: net user administrator /active: yes
Note: Please follow the same steps and type net user administrator /active: no to disable admin account after the troubleshooting is done
After enabling Built-in admin, please try with the steps below:
System file check is a utility built into the Operating System that will check for system file corruption The sfc /scannow command (System File Check) scans the integrity of all protected operating system files and replaces incorrect,
corrupted, changed, or damaged versions with the correct versions where possible.