slowing down of a comp could be many things, it could be that it needs windows reinstalling,
could be antivirus software slowing it down on the internet, or even third party firewalls if you have one.
it could be to many things running in the background,
you dont say what operating system you have m8 ,,
win 7 ? win xp ?? windows vista ??
more info is needed about the comp before any one can really help you..
first of all though .. click on the start button, then in the type box enter msconfig
when that opens , click on the startup tab and deselect everything in the list ,, then click ok or apply.. then restart the comp .. see if that works,,