I've downloaded and reinstalled the Steam version of Civilization (version 188.8.131.521 on Windows 7) along with all of its DLCs: everything is marked as "Installed" and the custom maps are all there and working. The game runs fine as well.
However, neither the main menu nor any of the sub-menus have the "Scenarios" menu. I've searched everywhere with no luck, and I have no way of accessing any of the DLC content.
How can I fix this?