Your motherboard needs DDR3 RAM, it doesn't matter what generation RAM the GPU uses as the motherboard interacts with the GPU through the PCIE slot.
That being said, there aren't many sensible upgrades for this platform. It's a 2012 platform that was never all that great for gaming, this is essentially a 2013 budget build. Hopefully you didn't pay much over $100 or so for this.
We're talking the new Modern Warfare, not the original 2007 one, correct? Assuming so, you're just at the minimum requirement for CPU but you're way under it for the GPU. The RAM is probably fine, though you do have a FrankenRAM situation in there since there's no possible matched-stick situation that would give you 20 GB of RAM. Since it sounds like there's likely a 2x8 kit and a 2x2 kit in there, I'd remove the extra four RAM and see if it has any positive impact on your situation overall.
You might get this running at 720p, but I can't imagine it would be a great experience.