Disk Defragmenter ...
When a file is stored to a disk on your pc, it is broken into tiny pieces each piece is stored in the first available sector of the disk.
When the disk starts fill up and more files are deleted certain random sectors become available on the disk, the files are no longer placed adjacent to one another. Thus, a file may be scattered across the disk (fragmented). This slows down the time for the files retrieval and slows down your pc speed.
To overcome this problem you have to defragment your hard disk.
All you have to do is click start menu\ program files \accessories\system tools and click defragmenter.

Select the drive you want to defragment. Exit all your other programs, then return to defragmenter and click ok
Note:- It might take many hours to complete. Especially if you haven't Defragmented your hard disk for a long time. If you are using your pc for typing and for games it is best to try to give Defragmenter at least once a week.
# After you use these tools a few times you should be able to know when your Pc needs a maintenance check up.