File Selection Screen Changed?

When I open a program, like Office, or go to upload a picture, etc., the box that comes up where you look in Finder and select the file, has changed. It used to be I would single click a file, and it would generate a preview in a column to the right. Now, I have to double click it, and I get no preview. Any thoughts? Thanks.

Sorry not bumping, just update: today, it worked again once, then reverted back to not showing previews.