Ok, here's something you can try. First download DirectX Eradicator from
here.Now you'll need the full versions of both 9.0b and 9.0c.
Once you get them extract them into two different temporary folders.
Copy and paste the following files from DX 9.0b temp folder to the DX 9.0c folder.
dxsetup.exedsetup32.dllDSETUP.dllNext run DX Eradicator and uninstall DirectX, when it's done run dxsetup from the 9.0c temp folder that you copied the files to. That should solve your problem.