Building a Computer, need parts, choose some for me?

I'm have a computer that my dad gave me, and i have removed all the parts, checked them all, put it back together and it works perfectly. But first let me give you some backround first.

First of all, i'm 13, second of all this a spare computer built in 2009, for my dads lawyer firm, its is no ways a gaming computer execpt for maybe the ram. Here are the specs:

CPU: Intel Core 2quad Q8200
Motherboard: Pegatron Benicia
Harddrive: 596 gb
Operating System: Windows 7 Ultimate (i'm keeping this, but might get linux)
Graphics Card: Intel g33/g31 Express Chipset Family (No longer sold).
RAM: 8gb of RAM.

Thats it, What i will need:
Most likely a new motherboard and cpu, a good graphics card, i'm gonna throw in 8gb more of ram, gonna keep the hardrive, its good enough, might buy a SSD. I will also need a case that will fit it, not overly big, and not to small, preferly cool looking.

Its needs to run Battlefield 4, Crysis 3 Minecraft, Farcry 3 and other games with NO LAG, on medium to standard quality settings. Keep the price tag as small as possible and use AMAZON! Thanks

Added (1). I built on with these specs
http://www.amazon.com/...IHL2WA8FM/

What i need is a LONG RANGE Wi-Fi chip that can fit this computer

You should probably get almost new everything except maybe the case and the hard drive unless it has no space left on it. Newegg.com is a great place to start

First off, you need to fix a budget. If you have a high budget go for Intel as it's supposedly "better" but AMD is relatively good for gaming and has improved lately. GPU can go for Radeon or GTX, I prefer the GTX 700's series because that's what I have but it might be a bit expensive. The motherboard will depend on your CPU. Also, you need to buy new RAM if you upgrade unless they are identical because it will cause some trouble. SSD are unnecessary for gaming and is only useful for loading Windows in like 10 seconds. The case - get a mid tower or lower and make sure include a cooling fan such as Hyper EVO. I picked out some parts for you:

http://pcpartpicker.com/p/2gSlF
Prices vary. Please do your research. The computer you built is much simpler. Don't get Linux. Since you're 13, be careful because of tendency to make mistakes.