It's very likely because you had a mod (villager stats utility, enhanced tooltips utility, New Editor/Editor Patch, etc) before you installed The Titans. Uninstall The Titans and Age of Mythology completely and erase all folders except savegame, rm and scenario in your C:/Program Files/Microsoft Games/Age of Mythology folder if you don't know exactly how to install the mod you have. If you want to be totally safe, delete C:/Program Files/Microsoft Games/Age of Mythology altogether, but you'll lose old saved games and custom maps. Mods to the original AoM hide new features added in The Titans - you may also be missing the buttons for Time Shift, Repeat Queue, etc.
I haven't watched the game but I assume you did research Secrets of the Titans; after you do that you should get a big round Titan Gate button at the top of the screen, just click it and click on the map to start making a Titan.