a) Open Scheduled Tasks (start/run/type: control schedtasks) and click on Add Scheduled Tasks to start the Scheduled Task Wizard. When you get to the list of applications, click Browse, and navigate to windows\system32\defrag.exe, and click Open.

b) select the frequency for the program to run monthly (usually). To defragment a disk, you'll need to supply the name and password for an account with administrative privileges (it means a user who has control over the computer, can install software, and can change user passwords). Check the box to open Advanced Settings when you're done.

c) In the Run box, add the letter of the drive to defragment so it looks like C:\windows\system32\defrag.exe c:

Note: if you have multiple partitions, you'll need to add a separate scheduled task for each one. A minimum of 15 percent free space on your hard disk is needed for Disk Defragmenter to run