Interactive logon failure+discarded username in Users tab

The OS is Win8.1

I am that computer's only user. So, there's only one account.

Sometime ago, I changed the username.

I followed your detailed tutorials (thank you).

I used the Win7 method of changing the value in the registry, from 0 to 1

When I enter username and password, the system tells me I've entered the wrong username and/or the wrong password.

I managed to get back to Windows by using a restore-point.

I noticed one thing: When I get into
Start, type "Give administrative rights to a domain-user" >> User Accounts >> tab "Users"
under "Username" I can see the previous, discarded username (Not the current one) and, beside it (under "Groups") it says "Group Administrators" There, I don't see, at all, the current, valid username.

In advance, thank you very much for your kind assistance