"The username or password is incorrect." without entering login details

The computer must be trying to log on with some details it has saved before it gives you a chance to login.

1. Run netplwiz either via the Start Menu or the Run Dialog ( + R)

2. Uncheck the box that says "Users must enter a user name and password to use this computer." and click "Apply" and then "OK".

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Source: http://answers.microsoft.com/en-us/windows/forum/windows_7-security/how-to-turn-on-automatic-logon-in-windows-7/99d4fe75-3f22-499b-85fc-c7a2c4f728af