It's happened to others as well. Here is the link:
http://forums.wmexperts.com/showthread.php?t=174771
Maybe someone there will eventually figure it out and explain why. Personally, I think it has something to do with a program or theme you might have installed, or a regedit that was made. Back track, and undo anything you have done since right before the problem started. Either that or back up everything, and do a hard reset.