I just recovered 2 separate Vista installations that would not reboot properly after apparently receiving a recent “important” update automatically. This may have been from a February 14th update and we’re only just learning about it. I have deduced, yet I’m not 100% sure, that I had installed Vista Service Pack 1 and other updates, but that recently, an auto-reboot revealed that the login screen was not displaying. One machine showed these symptoms yesterday after having been off for about a week when it auto-magically downloaded important updates and restarted. When it came back up, nothing appeared on the screen. I ended up returning to the oldest restore point to get back to a stable environment. Then I installed the updates separately. Now it works fine.
When my workstation began showing the same symptoms, I looked for the same solution. Long story short, after trying everything, I ended up restoring the last restore point and applying individual updates until it is almost back to where I want it. I think I’ll wait to reapply Service Pack 1. I’m just a little gun-shy.