My screen saver used to work displaying a folder of family photos. Now I just get a black screen after the designated time. Get the same thing in preview. Haven't done anything to it AFIK, Maybe the last batch of updates did something. Don't have any hidden updates, install all updtes. Don't think its any of my USB devices cause it used to work with everything plugged in.
More aboutscreensaver work
You need to select your custom screen saver and click apply.
I did click apply and still doesn't work. The windows default ones work fine thought.