Acer laptop locked.

I recently tried to set up a mail account on my Acer to help a friend to trouble shoot a problem with their mail. Now my login screen shows the email address of the account that I was trying to set up and is looking for a password and I cannot login. I tried to boot up in safe mode but but cannot.I have since managed to login using the password that I used in setting up the mail account. However my login screen now has the user name and email address of the mail account I was trying to set up as the login screen and my original username and password have disappeared. Same details in the user accounts.