This should help:
Click on start > run > type "control userpasswords2"
click OK. On the Users tab, clear the "Users must enter a
username and password to use this computer" check box and
click apply. Select the user you want to log on and click
OK. A dialog will appear that asks you what username and
password should be used to logon automatically, just
click OK.
Then, go to control panel > user accounts > change the
way users log on or off > uncheck the first box "use the
welcome screen."
Restart to make sure it worked.
