I'm the only user and my account has (had) administrator privileges. After a routine reboot, I logged into my account as usual, and soon found that I could not install software. I didn't have permission to write to the Program Files folder. I couldn't write to any folder outside of my home folder. I checked User Accounts in the Control Panel, and my account was now listed as a guest account. I have the built-n Guest account off, incidentally. I'm unable to change my account type back to administrator or create a new account because guests can't do much at all, really. Does anyone have any idea how to enable the built-in Administrator account from here or from a rescue disk? I should be able to fix my account easily from the Administrator account, no?
The changes I had made since last reboot that may have been responsible for the unintended demotion of my account are: I uninstalled the .NET framework 1.1. I deleted the ASP.NET user account that .NET 1.1 creates and leaves behind.