Image flickers when Previewing Thumbnails

When previewing thumbnails (pressing the space bar), the image now flickers—very annoying (the Cap key is not locked). Also, rotating a photo, I hit the key and nothing, then hit it again, and it turns twice, and I have to hit the previous key to correct it the way it should have been in the first command. Also, trying to figure out how to post something is confusing—lucky I copied my post first because it disappeared from the community several times.