Stuck on creating account

Force shutdown. Press and hold down the Power button until the computer shuts down. Wait 30 seconds, then do the following:

Repair the Drive for El Capitan or Later

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.
2. Wait until the Utility Menu appears.
3. Select Disk Utility and press the Continue button.
4. Then select the indented (usually, Macintosh HD) volume entry from the side list. 
5. Click on the First Aid button in the toolbar and wait for the Done button to activate. Click on it, then quit Disk Utility.
6. Select Restart from the Apple menu.

Try what you were doing again, if that is what happens upon the reboot.

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 can use the same Apple ID. What was stated is to use an account name that is not in use by any other account on the computer. If you have User_A already on the computer, then use a new name such as User_B.