Hi KunakornPruksakorn,
I'm Dyari. Thanks for reaching out. I will be happy to assist you in this regard.
May I know how did you create and grant admin access to the new account? From Settings > Account or from Computer Management?
Please click on Start > Type netplwiz and hit enter > Take a screenshot and post it back.
According to the screenshots that you have shared, your computer has only one local user account which is "Computer D..." and it seems that it does not have admin rights.
To grant this user admin rights, kindly try the steps below:
1-Right click on Start > Computer Management > Local users and Groups
2-Click on Groups > Double click on Administrators > Add > Type your user account which is "Computer D..."
3-Click OK
After that, this user should have admin rights.
About the Administrator user that you have found, it is a build-in administrator user. It did not appear on the login screen because it is Disabled "See the black down arrow on it). To enable it, double click on it > Untick the box " Account is disabled"
It will be enabled and appeared on login screen without any password.
To set password on it, right click on it > Set password
Please let me know if you need further assistance and keep me updated.
Stay safe