I am unable to complete defragging on my computer while running Windows XP (HE). There no programs running in the background and a minimal number of (unnecessary)programs are running in the task tray. I've disabled my Panda Platinum Internet Security program and any applications running in the Task Manager's application menu. I've even attempted defragging in Windows XP's "Safe Mode" without success. My HDD is not "Full" with at least 40% hard drive space available. What could be my problem?