It's a common misconception that Win7 has only DX 11. Win7 has three versions of Direct X.
The The vast majority of software and games still use DX9.
Sometimes one or more of the DX files in System 32, or SysWOW64f can become corrupt.
If you were able to play the game before on the same machine with the same Win7 install then
there may be a corrupt DX9 file.
The full Direct X redistributable (June 2010) is the best option in this case. This method overwrites the old files.
The download will unpack to a folder in a location of your choice. You then install from the
DXSetup.exe in the folder. After reinstalling DX you can delete this folder.
Download Details - Microsoft Download Center - DirectX Redist (June 2010)
If you are using a new Win7 install you can use the DirectX Web Installer instead of running the
whole package. It will install only those files that are 'missing'.
Download details: DirectX End-User Runtime
.