Your computer run slow because there are lot of temporary file so you should always clear the temp file from your computer and clear both temp file temp file from computer and internet temp file lets see how to do.
first go to start - Run - temp - hit Enter
there you will see lot of temp file clear all.
then do for internet temp file
go to start - Run - %temp% - hit Enter
there also you will see file delete that.
after that clear your cookies also in run command type cookies and hit Enter and clear that.
Its done Enjoy :)