Vista - Vista automatically logs off user account

Within the last 3 days or so, Vista has randomly (as far as I can tell) logged off my user account. This is problematic in that I don't use user accounts. I just have myself set as the admin and no one else uses the computer so I have no other user accounts. About 3 days ago I upgraded Vista to the latest service pack and I updated my Nvidia drivers to the latest WHQL drivers. I have my computer set to never log off, sleep, or activate a screen saver so I'm at a loss as to how to stop it.

Windows Vista Ultimate x64

Edit: it seems as though if I leave it alone for approximately a minute or two the account logs itself off. It's not so much random as I thought.

2nd Edit: It seems as there is a slight bug in Windows and I finally solved my problem. I have "None" selected as a screen saver but I checked another screen saver, "Blank," and next to it was a box checked with "On Resume display Startup Screen." Despite not having a screen saver set, Windows used the settings for a screen saver in this instance.

I believe the only way you can stop that is to turn off the password. I have always know windows to do this even in XP.

shor