How to disable the user selection – Windows 7

Need help on disabling the user selection on my windows 7, anyone know's how??
When I switch on my computer it is normally booting up to desktop. But now it is asking to select the user. There is only a user and I did not set any password for that. I don’t why this is happening. Even though there are no multiple users, why this is asking for select the user? I have checked the user account settings in control panel and I did not found anything to disable this option. I will be thankful for your help to get out of this problem.
