Sometimes fast running computer work slow and reason of this is

most software\ Program installed on your computer.
many unnecessary  things are reason make your computer slow
some things to helps speed up your computer.
 always temparary files are  created in your computer , as well as use of the Internet
many unnecessary files are created
                                                                                                                                                            delete the temparary files when you are free.
First start-all programs-accessories-run- then it will open a window
 Type this % temp% and the click ok button then all  temparry files we are show.
It is easy to delete