Well, if the folder is in Program Files, chances are that it was a "fully installed" program. In that case, the registry entries have probably been removed, so you would need to reinstall it. (Some programs just run locally and don't have registry entries, but they also probably wouldn't be located in the Program Files folder.) If you truly have a backup of the entire computer, there may be some way to restore the registry elements from your backup. It would be more difficult than simply reinstalling, and I don't personally know how to do that. I would suggestion reinstalling.