JetDefrag can only defrag files that are not in use. It cannot defrag the files that are in use, such as any programs that are running in the background. The best solution is to disable any screensavers or programs that are running in the background before starting the defrag utility. As an alternative, JetDefrag can also be run in Windows Safe mode in which no programs will be running in the background. Running JetDefrag in Safe Mode can be a faster alternative if you have many programs that automatically start at Windows startup.

To enter Windows Safe Mode, reboot your computer and immediately as the operating system begins to boot, press and hold the F8 key. Choose to enter Safe Mode. To exit Safe Mode reboot normally.