Although it's simple to allow the computer to automatically load to your main administrative user, if something goes wrong with that user's profile, you're sunk.. In you case, that may be exactly what happened.. Something may have become corrupted in the user's profile and it's not behaving as it should.. Or in some cases, a setting may have changed, such as a new password was created for the user, or the setting for Control Panel-User Accounts-Change the way users logon or off-"Welcome Screen" may have been altered.. (Or open a Run line, type "control userpasswords2" and find whether "users must enter a user name and password to use this computer")
Either way, as long as you've got a second user login, with admin rights and passworded, on the computer, it will help you recover problems should they arise.
Hope this helps.
While I plan on changing this in the future, in the past my family have all used the computer and never had a need for separate users. As a result of this, when you queue up the computer, it opened immediately to Windows Explorer on the desktop. Recently, however, through methods which remain opaque to me, the central user "family" was locked out. There isn't any password or anything, it just says "locked" and requires you to click on the user to access it. As far as problems go, this isn't a huge one, but I'm curious as to how it happened and if there's a simply way to unlock the user so that when the computer wakes up, it simply opens to explorer like it used to.