Excerpt from the article: "As computers get older, it becomes more and more difficult to get them to run the latest and greatest hardware and software. The newest games are notoriously bad about not running on older hardware. They generally require the fastest CPU, video card, and a ton of RAM in order just to run properly.
Sometimes older computers just don't appear to be
running as fast as they use to, or they just stop meeting your needs.
When this happens you're faced with the choice of upgrading it, or just
replacing it all together.
Before replacing your computer with a
new one, there might be a few things that you can do to extend the life
of the existing hardware. You might be able to optimize your computer
to run more efficiently, or replace/add some new components to meet your
needs and get a few more years out of it." (read the rest of the article)