New
#11
It is really easy.
Tick the box that says "Users must enter a user name and password to use this computer" and press apply.
Untick the box that says "Users must enter a user name and password to use this computer" and press apply
Tick again the box that says "Users must enter a user name and password to use this computer" and press apply
Then (assuming you don't want to enter a password), yet again, untick the box that says "Users must enter a user name and password to use this computer"
The idea here is to make it forget the old PC name/user credentials and remember the new one. When you "untick" the box it makes you put in your password.
There is no risk to do this and it only takes a minute. Worst case is you type the password wrong and it doesn't work in which case you can try again.