First way is to remove all additional users on the computer. While you're also in user accounts under the control panel, click the option to change the way users log on or off, and make sure it is set to use the welcome screen. Also remove any password on the user account.
Finally, if still not working, like some programs like Quickbooks or Ghost create a extra hidden user account, you'll need to google tweakui, and download it off of Microsoft's website, install it, and in there has an auto-logon option that is guaranteed to work.