My Computer Won't Use DX11 anymore

Kadoken

I've had this computer for a while and it has worked swimmingly especially when I upgraded it. However, ever since I installed Civilization 5, I've noticed that I can't use DX11 for games anymore. I can't switch settings to DX11 in Shogun 2. No matter how hard I try, I can't get Civ 5 to run in DX11. I have the updated (fully) drivers, a good videocard (ATI6870) and a great processor with an aftermarket cooler (AMD 975 quad core).

Does anyone know how to fix this? I have tried putting Steam in different compatibility modes ever since Civ 5 refused to play in DX11. I don't know what to do.

Great Scott

I would check here first. http://windows.microsoft.com/en-US/windows7/Which-version-of-DirectX-is-on-your-computer

I assume that you've already tried running DXdiag and tried downloading the latest DirectX redistributable?

EDIT: Have you read/tried this? http://forums.civfanatics.com/showthread.php?t=464486