Originally Posted by
Glycerius
I would see a mod as a possible cause. Perhaps the file tree for the campaign is wrong when a folder was moved, but then the whole game might not start. It certain cannot find any campaign. If the files are where they should be (drive\Program Files\Activision\Rome - Total War\bi\data\world\maps\campaign\barbarian_invasion), then check all files are there, and check inside the files. If it cannot be set right, a reinstallation, with any files required backed up, is necessary.