I am running Photoshop CC on Windows8. I can have Windows associate many file types with Photoshop, such as .png and .jpg. This does not work with .psd files! Windows sees Photoshop as a possible program to open .psd files but when I choose it the dialog box disappears and the link is not established. I can open .psd files from within Photoshop. Windows8 also does not create thumbnail previews of .psd files, although Bridge CC does.
If you are sick as me of not being able to view PSD thumbnails in Windows anymore? I found this great OpenSource application Sagethumbs that that allows you to preview image formats directly in Windows Explorer. I have tested it on Windows 8.1 and it works like a charm - http://osmoney.com/multimedia/sagethumbs