I have been running Google Photos Screensaver on Windows 8 without any trouble for the past month or so. In the past few days the screensaver failed to come on. Whatever I was working on was still there when I came back to my computer hours later.
I tried testing the preview button. The screen goes blank, something flickers and then it goes back to the desktop that was there before I hit preview. If I change the screen saver to something else (eg. Mystify) then preview works.
I am using Picasa 3.9.0
The following failed to fix the problem
I updated my nVidia GeForce GT 545 drivers. I tried the preview with my mouse unplugged and then switched to my keyboard being unplugged.