Have you ever wondered why if you dont defrag your computer gets slow and will eventually crash? well its becuase your computer doesent always know where to put files and them they need to be cleaned like a room in a house.
Dont ever use the onboard windows defragmenter it will crash your system as quick as on board disk cleanup. use diskeeper lite its free and on the main page of the site. I have tried many this is the easiest amongst the free defgamnenters right now but it works well and wonk crash your system. Good Luck here is a link to diskeeper lite.
http://www.highlevelweb.com/index.php?option=com_content&task=view&id=15&Itemid=49