Have you installed this?
Also switch your video plugin to DirectX 10 or 9 if your system doesn't support 11.
i5 3750k @4.2GHz | Nvidia GTX 670 2GB | 16GB Corsair DDR3 RAM | Windows 7 64-bit
which one do i download? coz im using dx11
What do you mean which one? After you run the updater Khalan linked you to, you just select everything it finds that needs updating and installs it.
And you're not using DX11, your system has DX9,DX10 and DX11 and depending on the application it uses what is needed.
Just a quick note if you are still getting problems, if you have the RC of win7 you can't use dx11, only in the retail version is dx11 supported
CPU: AMD Phenom II @3.2GHZ X4
RAM: 4GB DDR3 memory @1600MHZ
GPU: ATI Radeon 4850 1GB DDR3
OS: Win XP Pro 64bit /Win 7 64bit RC
Windows 7 RC did come with DX11 same as the final.
Core i5 3570k -- Geforce GTX 670 -- Windows 7 x64