I have been getting a lot of shading problems (http://www.microsoft.com/en-us/download/details.aspx?id=35) I was told by an ASUS support guy that it's a DX problem. I tried downloading http://www.microsoft.com/en-us/download/details.aspx?id=35 but it told me that I already have DX and that no new install is required. How do I reinstall DX without reinstalling windows?