Deleted account still being detected (OS X El Capitan) I recently got a Macbook and easily set up my user account (admin), plus a standard and guest account. 

One day, I opened the computer and the screen was frozen. After waiting a few mins, I forcefully shut it down by holding the power button. When I turned it on, my account was gone, only the standard and guest accounts were left.

I logged in to the standard account. I could see my admin account on the User list. However, no matter what I tried, I could not access it, it just wouldn't show up on the login screen. I ended up changing the standard account to an admin account and deleting my original admin account completely. 

A few days later, I tried to create a new admin account with my name. However, when I put my name in, it said that this name was being used by another user, even though I had completely deleted it before. 

Any idea how to solve this?
Open up terminal from /Applications/Utilities and run this command sudo sysadminctl -deleteUser username
Replace the word username with the shortname of the account you’re trying to delete. 
This will delete the actual account and it’s home folder so be sure you don’t need anything from that account.