They're probably gonna pump this into the tech support forum, but yes, what he said. Try to reinstall it. If you've copied or moved the game folder since then it won't work. I wish they'd add an option to search for the .exe or just make the executable a self extracting archive so those of us who know what we're doing can just unzip it wherever we have the game at the moment(external drive).
@Eragon Which will mean you need to register your games(or at least a Rome one I think) or you won't be able to read anything after they move it.