Ok, there is a bug in Windows 7. Something minor but it makes your video card believe you only have Direct X 10.1 installed. You need to download a hotfix from Microsoft to fix it. Once you download the hotfix you need to uninstall all of your Nvidia drivers and reinstall them and you'll have direct x 11. Let me get the hotfix for you. http://support.microsoft.com/kb/975243/
there you go. Ok you have to have an email....they will send it to your email and then you can download it from your email. I had the same exact problem with my Windows 7. Just make sure to uninstall and reinstall your Nvidia drivers after installing this hotfix. Let me know how it goes.