There's only one item I can think of that you can try and that's logging in as ROOT, removing Administrator from your Account, giving yourself Administrator permissions again, and then never using ROOT again. Here's a way you can try to get into the user ROOT.
1. Start the computer up in Single User-Mode: When turning on the computer press and hold Command+S till it takes you to the black screen with white text.
2. It tells you, to start the computer type in these commands... type in the one that says mount -rw / or something like that.
3a. Now I'm not sure if you can do this here or not, but type in: passwd
And set the password you'd like to use.
3b. If 3a didn't work, type in the command (it shows you above) sh /etc/....
While this is loading up keep typing in passwd, till it asks you for the password (it takes some timing, and you wanna keep the password short, simple, and easy. I've done this one on an iBook G4 and 2 PowerMac G5s. It can be done.
4. Instead of logging in as your user, log into root (username: root password: whatever you typed in in 3a or 3b).
5. Open System Preferences and try to change your user permissions.
Try that, and post your results.