If you go to nVidia Control Panel and reset your Global 3d Settings. Anything?
As was stated, did you try latest drivers? Tick "Clean Install"
Here's about the only difference inbetween our two systems (other than OS and massive OCing *oh and a ton more RAM... so maybe more diff than I want to think) I still have a dinosaur (SLI but it isn't working with defaults, need to force render 2.. haven't even tested it yet)
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This is pretty "experimental" and I doubt most of these settings even work (i.e. do anything)... but try it
Open Notepad.
Copy and Paste this:
RenderDevice.ForceRenderAheadLimit 1
PerfOverlay.DrawGraph 0
PerfOverlay.DrawFps 1
PostProcess.DofMethod 0
PostProcess.BlurMethod 0
PostProcess.DynamicAOEnable 0
PostProcess.DynamicAOMethod 0
GameTime.MaxVariableFps 60
Render.VSyncFlashTestEnable 0
WorldRender.TransparencyShadowmapsEnable 0
WorldRender.MotionBlurEnable 0
WorldRender.MotionForceOn 0
WorldRender.SpotLightShadowmapEnable 0
WorldRender.SpotlightShadowmapResolution 256
WorldRender.LightTileCsPathEnable 0
RenderDevice.Dx11Enable 0
RenderDevice.Dx11Dot1Enable 0
RenderDevice.Dx11Dot1RuntimeEnable 0
RenderDevice.VSyncEnable 0
RenderDevice.TripleBufferingEnable 0
((I have no clue how many of those are actually being read... I know for a fact some are though))
Save it as "user.cfg"
You cannot have user.cfg.txt enable "View Extentions" from Folder Options in Control Panel
Put it in your PvZ directory
\\Origin Games\Plants vs Zombies Garden Warfare
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CPU Unpark has been used in BF4 for a long time, good responses.
http://www.coderbag.com/Programming-C/Disable-CPU-Core-Parking-Utility
*Since you have low RAM mise well mention it:
RAMMap -> Clear Standby (probably does nothing of value)
http://technet.microsoft.com/en-us/sysinternals/ff700229.aspx