Lost control

Hi, I'm a newbie to major geeks. I have found a lot of helpful information already. I'm hoping the forums may prove as helpful . I have been taken over by something that has inserted itself as administrator of windows. I am "protected" by Norton 360, which wass no help at all. Saturday afternoon, after surfing the web and a couple newsgroups, xnews stopped working, the shortcut and executable file had disappeared from the directory.
Next, Norton said it sensed a system issue, but it was unable to do anything about it (much like Norton on-line tech support). After a short time of the hard drive running intermittantly doing God knows what (task manager is locked, I can't open it to see what is loaded or running) everything finally ground to a halt. Maybe that's an exageration, but not much. I can't start Norton, permission is denied by administrator. I downloaded and installed AVG after the problem started but I am not permitted to start it. I am totally frustrated by this since it seems to have blocked me from doing anything to overcome it. I have a recent back-up I can use to restore my files if I have to reformat and reinstall everything, but I don't know if something may still be lurking out there to take over my fresh install. Not only that, I don't know if windows will allow me since I'm not the administrator? Merry Christmas!