Your my music folder location is C:\user\ (username) and iTunes location is C:\Program Files ?
One more question ... How many hard disks do you have, and are the musics stored anywhere other than the disk containing C drive ?
If so , Download take ownership.zip from the second post of the thread, unzip it, there is a file take ownership.reg. Run it as admin and merge it. then there is "take ownership" in your right click context menu.
Right click on your music folders, and take ownership (including my music). Then you should be able to add musics to your iTunes library .
This process worked for me for two times . I have stored all musics in a disk other than the disk with C drive. So for two clean installations, I tunes refused to add musics .