I have a custom build computer, and all my components are relatively new and proficient, yet I experience a lot of slow performance, especially when it comes to gaming. Most of the time I have to turn down video settings, even though I have a nice graphics card, because it makes all other programs (firefox, itunes, etc) lag very badly when running simultaneously. I run my anti-virus programs semi-regularly so I don't think I have any viruses, so what could I do to increase my performance?