If you are having problems with thumbnails not showing up while using News Magazine Theme 640, there are a number of possible reasons. There are many of posts on the site dealing with the thumbnail issues users are experiencing. Not every solution will work for every situation because not everyone is dealing with the same reasons for the thumbnails not working. A newly discovered cause of thumbnails showing up with the default no image available graphic is filenames with more than one dot. Example this_is_my.file_name.jpg
As a general rule you should not have a filename with more than one dot. It will work in some instances but not in others so the best practice is to avoid multiple dots in your filename. Definitely if you are going to use News Magazine Theme 640 do not use filenames with more than one dot and make sure the dot is the one that precedes the extension like .jpg, .gif, .png etc.