To help you I need to get some more information about the files and your computer.
Are you opening a large Word document or a large PowerPoint document? Do this file(s) has a lot of images?
Do you have other memory hungry opened on your machine while you try to open these files?
Did you receive this file via Email? It is possible that the person who created this file added the images as references and did not provide the images which may cause them not to appear.