there is no admin listed in users and groups

Restore Admin Privileges

This procedure should restore admin privileges to an account that has lost those privileges. This procedure is only needed if you don’t have another account that has admin privileges.

Section One

Boot Using Command+R keys:

1. Restart the computer.

2. Immediately after the chime press and hold down the

"COMMAND" and the "R" keys together.

3. Release the keys when the Utilities Menu appears.

If you use FileVault 2 then open Disk Utility, select the protected volume and click on the Unlock button in the toolbar. You will be asked for your admin password. Quit Disk Utility.

Open Terminal from the Utilities' menu in the main menubar. At the prompt enter the following command:

resetpassword

Press RETURN.

A window opens to Reset Password. Select your startup volume. From the menu labeled Select the user account select System Administrator (root). Follow the prompts for setting a password. Be sure you write down the new password so you don’t forget it.

Now, from the menubar select the Restart… option.

Section Two

If you are using FileVault then log in as usual, then select Log Out… From the menubar or press SHIFT-COMMAND-Q. Don’t RESTART. You will be returned to the Login screen.

At the login screen click Other… Enter root in the Name field. Enter the password you set up from Section One in the Password field. This should have you logged in as the “root” user. While in “root” be careful what you type or enter. Carefully follow these instructions.

Open Users & Groups preferences panel. Select your normal administrator account from the list of users and check the box labeled, Allow the user to administer this computer. You will be prompted to restart. After the login window appears, log in as yourself—not as root.

Your administrator status should now be restored.

Section Three

You should disable the root user if you enabled it. Follow the instructions in OS X Mountain Lion- Enable and disable the root user under the heading, “Disable the root user.” You will be asked to authenticate in Directory Utility as root with the password you set in the first section. The linked article also works in Mountain Lion and Yosemite.

How to Create a New User Account if You Cannot Access Your Admin Account

Reboot the computer. At 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 for it to finish.

Enter the following lines at the command prompt pressing RETURN after each:

mount -uw /

rm /var/db/.applesetupdone

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 the admin user account that already exists on the system. When you finish the Setup Assistant, it will automatically log you into the new account.

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.

From Standard to Administrator - Hack Mac

How To Create A New Administrator Account - Hack Mac

As per this article OS X El Capitan: Set up users on your Mac

Standard: Standard users are set up by an administrator. A standard user can install apps and change settings for his or her own use. Standard users can’t add other users or change other users’ settings.

Convert a standard or managed user to an administrator

1. Choose Apple menu > System Preferences, then click Users & Groups.
2. Click the lock icon to unlock it, then enter an administrator name and password.
3. Select a standard user or managed user in the list of users, then select “Allow user to administer this computer.”