After login my macbook keeps asking for username and password. I remember my username and pass but it isn't being accepted.

Were these configured when you initially set up the computer? The name you use for your Home folder is the username. Your entered full name at setup can also be used for the username.

Forgot Your Account Password

For Lion or later

Reset a Mac OS X 10.7 Lion Password

OS X Mountain Lion- Reset a login password,

OS X Mavericks- Solve password problems,

OS X Yosemite- Reset a login password.

El Capitan Password Reset.

macOS Sierra-Reset a login password.

Change or reset the password of a macOS user account - Apple Support.

When you open your Mac in the display screen name and password field is shown and you can see your correct admin name and even you try to enter the correct password and it is not accepting , the only way to enter in Mac is update the keychain password as login password is kept same as keychain password for an administrator .

See this Keychain for Mac: login keychain

Try this method -

Close all applications and shut down the computer , press command , R and power key simultaneously , release only power key and keep on holding command and R key until apple logo appears , the bar starts loading let it be completed .

Select the language as English , go to utilities on top menu bar > Utilities > Terminal execute a command resetpassword and click on enter key .

Window appears , select your admin name it will prompt to enter Apple ID and password .

Once you enter the credentials , two options will be shown ( a ) previous ( b ) next , click on next . Some fields will appear . New password ………. Verify password ………. Password hint ………. Enter your new password in two empty fields and keep password hint as empty ( optional ) . It will again prompt two options ( a ) previous ( b ) next Click on next .

Then it will prompt to restart the computer , so after restarting the machine .Pop - up will appear

The system was unable to unlock your login keychain , if you remember your old password you can update the keychain password .

If you do not remember your old password , you can create a new login keychain or choose to leave the login keychain using a different password .

Would you like to update the password , create a new keychain , or continue the login ?

A window will appear on your desktop .

( a ) continue login .

( b) create new keychain .

( c ) update keychain password .

Click on update keychain password , then log out from your computer .

When you again login in the fields enter your “ admin name “ and “ old admin password “ , so that new password will be updated with login keychain .

Hence , the admin password is changed with the help of “ Recovery mode “ only .

As you remember the old password and admin name correctly , creating new login keychain should be avoided .

Do an archive installation it will overwrite on the previous version , use App Store see this article How to reinstall macOS - Apple Support

And the latest version is Mac OS high Sierra 10.13.3 How to download macOS High Sierra - Apple Support

When the person itself deleted his original account by clicking on minus ( a pop up window appears the correct way is choose last option ) so that account home folder is fully erased see this article macOS Sierra: Delete a user or group

And if he choose second last option

Leave the user’s home folder as is: Select “Don’t change the home folder.” The user’s documents and information remain and the user can be restored later if needed. The home folder remains in /Users/. or selected as first option .

This home folder can be retained see this article macOS Sierra: Restore a deleted user

And read this article macOS Sierra: Set up users, guests, and groups on your Mac

never tried the sudo command as John Galt has solved it , if original admin account is deleted by the administrator itself .

This happened to someone I was helping. The admin account disappeared after he tried to upgrade to High Sierra. His wife was left on however as a standard user. Nothing could be adjusted or changed as the lock on users and groups required his sign in credentials, which weren't accepted. Friend called me to help out, so I headed over "blind" & dependent on feedback from him on how this may have been set in motion....this was the first time I've dealt with one of the users left on the acct with data intact and furthermore, it appeared her name had replaced his minus admin privileges. Other than trying to upgrade, he couldn't think of anything else that may have initiated the loss of his admin acct.

I initiated single user sign on, the commands populated automatically. Set up assistant did not begin (I almost force started Setup Assistant but I took a detour before attempting that). I went back to his screen - logging in with his wife's name & password to look into the situation more. While in the system looking at data, etc, I had him log into iCloud, which stated incorrect pw for it. I had him change it. His data suddenly began to populate, icons were now clear & apps were fully functional, etc, but he still wasn't listed as admin. & the lock on users remained.

Still being on Sierra, he wanted to upgrade to High Sierra right away & felt confident in doing so regardless. After loads of time & energy invested in ensuring things were backed up, etc, he initiated the upgrade. I had to get to a meeting as well, so I allowed him to go forth and initiate the ugrade & I left him with info to sign in with his Apple ID & password to add himself back & gain admin privileges once again, then edit his user info and his wife's after logging in as admin once again, with his reassurance he was "very okay" with the rest of it..

But...true to form when I have to leave the finishing bits in another's care, I get to thinking about it and become a bit anxious. I hope I left him with proper resources and moreover, I hope I did all I was supposed to prior to installing High Sierra. I am checking in Thursday but it's getting to me..

With all of this in mind, can you think of anything I may have missed? I'd hate to back track bc I missed a simple yet crucial step. But, if I have to, I will of course.

Thanks in advance for the time, L ~

Are you using your Apple ID and password or your user name and password? It needs your user name and password.

There is no user , and this screen shot shows that you are using Mac OS X El Capitan or previous version , you must reinstall the os .

Welcome .

User Account – Add New Admin In Single User Mode