The question mark indicates that the file has been renamed, moved or deleted outside of the Organizer. It is therefore considered to be a "missing file". All that is showing up in the Organizer is a small thumbnail of the missing file. If you have deleted the file from your computer, you can simply delete the thumbnail with the question mark from the Organizer. Otherwise, you have to reconnect the thumbnail with its new location or renamed version. The best way to do this is to do a Find>All missing files. Once the search has been completed, you can double-click on a file and you will be given a dialog to reconnect it.