1)Check for viruses some good free AV programs are Malwarebytes or Comodo. 2) use disk clean up under all programs > accessories > system tools 3) use disk defrag under all programs > accessories > system tools 4) limit what programs run at startup. click start > in the search box type msconfig > startup and disable all programs you do not use often from auto starting when the pc starts. 5) right click your local disk in the computer tab, go to properties > tools and run error checking. 6) check your ram and CPU usage CTRL + ALT + DEL > performance check if your CPU and ram usage are under 80%. High CPU or ram usage can also be signs of a virus, if you have run a virus check and still have high RAM/CPU usage it may be time for a new PC. All of these things can cause a slow down in your PC and often it is difficult to pinpoint the problem without testing all of these options in order.