I can install, patch and run the base game fine but the adventure pack confuses me, since it needed the main game to play I installed it in the same folder except that seems to have deleted the main game ext file so i can load up the launcher but the game itself wont.
Both main game and exp are physical copies.

Any help appreciated

If installed correctly, the adventure pack (pirates and nobles) should be in a folder called EP1 inside the main "the sims medieval" folder. In there look for Game\Bin to see if u can find the relevant exec files you need to run the game.