Spyware and Viruses
Viruses can slow down the performance of your computer and make it impossible for a small task to run. Spyware tracks your browsing habits and sends you unsolicited advertising pop-ups. A Keyboard logger copies your password and transmit it to hundreds of hackers who are ready to steal your financial information.
Technological Advancements
Technology changes rapidly and trends suggest that every three years you need to upgrade your PC. What is said about Technology maybe true, However, It is possible to Fine Tune your PC and with a reasonable upgrade keep it running for much longer than three years.