I've been playing around with Vista for a couple weeks now off and on. This morning I decided to see what my user experience would be if I "demoted" my user account from the Administrators group to the Users group. I did so, rebooted (I had just loaded a new video driver as well), and logged back in. At that point Windows popped up a bubble saying that it had multiple security issues no AV and out-of-date Windows Defender definitions. I opened Windows Defender and told it to update it definitions at which point it popped up a dialog asking for an admin password to continue...
At this point I realized that I had just been INCREDIBLY stupid. Not only was there only one enabled user account on this machine (mine), but I had just dropped that account out of the Administrators group. That means that there is no admin password to give it of any sort.
Just to make sure I've been clear there are three users on the computer: Administrator, Guest, and <mine>. Administrator and Guest are disabled (just like when I first installed Vista), and my account is currently only in the Users group.
Is there a way to recover from this or do I have to reload Vista?
TIA, Jason

Unless you made the Administrator account active (it is disabled by default) then you will not be able to recover from this error. As you no longer have any admin level access to your PC. Mike Brannigan

Mike Brannigan wrote:

According to this: blogs.msdn.com/windowsvistasecurity/default.aspx
"On non-domain joined computers, when there is at least one enabled local administrator account, safe mode will not allow logon with the disabled built-in administrator account. Instead, any local administrator account can be used to logon. If the last local administrator account is inadvertently demoted, disabled or deleted, safe mode will allow the disabled built-in administrator account to logon for disaster recovery."
So if I read this correctly, the OP can go into Safe Mode and log in with the built-in Administrator account which will be enabled for this session only.
Malke Elephant Boy Computers elephantboycomputers.com "Don't Panic!" MS-MVP Windows - Shell/User

"Malke"

Interesting and well worth a test. The OP did not say if the machine was stand alone - but I assume so - so maybe Safe Mode is his savior.
Mike Brannigan