XP Media logon.

My daughtter has a Dell computer with XP Media, when starting up she is presented with a box that has her name and password entered.
As she did not have a password when it was setup she used to just press enter and it continued to boot up. Now it says it does not recognise the password entered and refuses to go any further.
Is there any way of returning it to the original position.
I would be greatful for any advice.