Images don't display in print layout view

When writing a manuscript or grant, normally if I insert a jpeg, tif, or png file into the Wprd document, the image  is displayed.  All of a sudden, then images aren't being displayed.  If I resize the image by dragging a handle, the image appears in the background but disappears when I let go of the handle.  Everything prints fine.  There no red X in the box the image is in (though why it's in a box, I don't know either).  This happens whether I do 'Insert/picture', 'insert/object' or simply drag and drop the image.  In 'Options/advanced/show document content', I have 'show background colors and images in print layout view' checked, as well as "show picture placeholders," and "show drawings and text boxes on screen."  Previously, all the images were there, but I've apparently done something.  Suggestions, please.  Thanks.