Over time, files stored on your hard drive becom fragmented on the hard drive and the computer begins to slow down as it takes more and more time to access the data in these files.  It is a good idea to periodically defragment your hard drive.  The more you install, delete and modify programs on your hard drive, the more fragmented it becomes.  When working with files, Windows stores file data in different parts of the hard drive.  Defragmenting your drive cleans things up by rearranging files to store individual file data together as much as possible, thereby making it more efficient for the computer to interact with these files.

Windows XP / Vista

1. Click the START button.
2. Go To All Programs.
3. Select Accessories.
4. Select System Tools.
5. Select the Disk Defragment tool from the list.

Defragging may take a while depending on your system speed and the size of your hard drive.  You may want to leave it running when you go to bed, it should be finished before you get up in the morning.