How did you messed up your computer?.. Anyway, perhaps (if DirectX is still installed) You should remove it first.. Start --> configurations --> Control panel (if i am correct) and software remove, whatever.. and search DirectX in the list.. and remove it
you cant uninstall direct x, when you install it, you have it forever, atleast thats what i know. I know this becuase my friend installed Dx9.0c on his computer and his video card only supports Dx8, so i tried to install Dx8 and i read somewhere that you cant install an older version of Dx over a newer version, and i also learned that you cant uninstall it.
So if you could please post your version of Direct X then I would be glad to help you.