First thought is software interferring. Anything from antivirus to malware to overlay programs.
Try disabling any overlay programs like RiviaTuner, Fraps, TS overlay etc etc. Origin in Game has issues with extra overlays. OiG is needed for shift+F1 easy invite friends and coin shop other you can disable it to try?
Clean Boot
http://support.microsoft.com/kb/929135
----
This is just throwing it out there... don't really think it'll fix anything but who knows crazy things happen. Much of it isn't even being read/used I don't think.
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
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
GameTime.MaxVariableFps 60
Save it as "user.cfg"
You cannot have user.cfg.txt
enable "View Extentions of Known File Types" from Folder Options in Control Panel
Put it in your PvZ directory
\\Origin Games\Plants vs Zombies Garden Warfare
---------
*edit - You could try latest beta drive from AMD.