Mac os

Press and hold down the Power button until the computer shuts down. Wait 30 seconds. Restart the computer. If the computer still doesn't startup, then try this:

Reinstall El Capitan or Later Without Erasing Drive

Please be sure you back up, if possible.

1. Restart the computer. Immediately, at or before the chime, hold down the Command and R keys until the Apple logo and progress bar appear. Wait until the Utility Menu appears.
2. Select Disk Utility and click on the Continue button.
3. Select the indented (usually, Macintosh HD) volume entry from the side list.
4. Click on the First Aid button in Disk Utility's toolbar. Wait until the Done button activates, then click on it.
5. Quit Disk Utility and return to the Utility Menu.
6. Select Install OS X and click on the Continue button.

Try this, instead.

How to Create a New Admin User Account, if You Have None

Reboot the computer. At or before the chime, press and hold down the COMMAND-S keys to start into Single-user Mode. You will boot to a black screen with scrolling white text, release the keys and wait until it finishes. Enter the following lines at the command prompt pressing RETURN after each:

    mount -uw /

               ^     ^  Note spaces

    rm /var/db/.applesetupdone 

        ^    Note space

    reboot

After you reboot the computer you will be taken to the Setup Assistant. When you get to the point where you are asked to set up your new user account, create a new admin account. Be sure to name this user account something different than any other account that already exists on the system. When you finish the Setup Assistant, it will automatically log you into the new account.

You need do nothing more. Log into the Admin account only when you need to, such as installing or upgrading software. Log into the Standard account for your normal computer uses. If you prefer using just one account, the admin account, then you will need to make some changes as discussed below.

You can transfer your files from the old account to the new one. See Transferring files from one User Account to another. Once you have moved all your files into your new account, you can delete the old account using Accounts or Users & Groups preferences.

You need to install the version of macOS that came with the computer from the factory when new. What model do you have? I need to know it's year and when during that year (Early, Mid, or Late.) You need to start with the factory version before you can upgrade to High Sierra. This is always required for a blank drive. That is what you have but did not prepare a replacement of the OS. Do you have backups?

????

I did not understand the earlier post because I thought your issue was solved. If you need to reset your Admin password: Change or reset the password of a macOS user account - Apple Support.