Over the course of using a computer, documents, pictures, programs, and everything else get stored on your computer's hard drive. These files can be scattered all over the hard drive, and can slow performance of the computer as a whole. To defragment your hard drive, click the "Start" button and then click "My Computer". When that box opens, RIGHT click on your hard drive (Letter C:) and click "Properties". This will prompt you with a box with several tabs. Click the "Tools": tab and you will have three options. Each tool can be used for diagnostic purposes, but for now, click "Defragment Now". On the box that comes up click "Defragment" and then let it go to work. This process takes some time, and is very processor intensive, so do not does this while you are trying to use the computer for other tasks.