So I'm looking to either severely upgrade my old computer or build basically a new one inside the case. What I have currently (don't use it anymore) is a Gateway 4720-03. http://m.newegg.com/Product/index?itemnumber=N82E16883113078 . What I'm looking to do is salvage any parts of it that I can and replace the ones that are outdated in order to build a good gaming/recording PC. My budget is around $500 preferably but if needed I'm willing to go to around $800. I don't know the first thing about computer hardware so just let me know specifically what parts (if any) are okay to keep and which parts I need to replace (as well as what to replace them with).