You say "in Photoshop CC" but the screenshot is of Windows Explorer file selection so what isn't working is some sort of Windows codec to render DNGs. You'd see the same lack of thumbnails if you opened Windows Explorer on a folder of PSD or raw files.
Did you have a Microsoft Raw or DNG Codec installed? There used to be one, but I don't know if there is currently.
I use the Fast Picture Viewer Codec Pack on my computer to see various image thumbnails:
Thank you. Meanwhile, I downloaded Windows 10 and now I see DSC, raw thumbnails but NOT PSD thumbnails.