Boot up

I need help upgrading my pc for gaming, my current specs are: gpu- amd 7770 1gb vram cpu- intel core 2 quad q6600 motherboard- intel dg31pr psu- 550wat (not sure what brand) ram- 3gb 2ddr hd- 1tb I want to spend under $300, i need more ram i would have to get a new a motherboard, then also a new...