Secondly, you may have a lot of unnecessary background programs running that you didn't even know you had. These can eat up your PCs RAM and reduce it's responsiveness. Click Start > Run > and type "msconfig" in the box and press enter. First, click the Startup tab. Here you will see a list of programs that are set to start when you load Windows. Look at their descriptions. Many of them can be safely disabled by unchecking the box next to them, especially updates programs from the likes of Adobe, Quicktime, Google etc.
Next click the Services tab and tick the box near the bottom that says "Hide all Microsoft Services". Again you will see a list of services that start - many of which you might find you don't need. Once you have made your changes here, choose to exit and restart. If you disable something you later want back, it is simply a case of running MSconfig again and re-checking the box. You can also try
http://www.malwarebytes.org/startuplite.php
From the same company that makes Malwarebytes. This will do the above process automatically for known unnecessary startup items, but is nowhere near as comprehensive as doing it yourself.