PC rebuild help

[FoRPoP]

I am rebuilding my old PC for my brother(he will use it for gaming). I want to make it the best it can be without changing the motherboard. I pretty much upgraded everything besides the GPU. I don't understand how does GPU compatibility works, so thats a part that I need help for.
PC specs:
MOBO: AsusTek P5LD2-x/1333
CPU: Intel Core 2 Duo E8600 3.33GHz
RAM: 2x2gb DDR2
GPU: ATI Radeon 3600 series
I don't plan on overclocking. I would like some suggestion on a GPU(the price doesn't matter).
Thanks in advance!

 

[MasterDell]

Honestly, a complete new system would be better.. If I recommend a GPU, it's just going to be completely bottle-necked by the CPU.

But since you came for a GPU recommendation, this is what you will need:

PCPartPicker part list / Price breakdown by merchant

Video Card: MSI GeForce GTX 960 2GB Video Card ($184.99 @ SuperBiiz)
Power Supply: Antec 450W ATX Power Supply ($27.99 @ SuperBiiz)
Total: $212.98
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-08-05 17:32 EDT-0400

 

[FoRPoP]

Thank you very much, I will take your advice for a complete new system into consideration.

 

[MasterDell]

Glad I could help