If your display uses dpms, that could be why the screen is blanking.
I'm unsure as to why you'd want to use fluxbox in a KDE distribution? You'd be better off with a lighter distribution and just installing xorg, fluxbox and whatever else you need from scratch...
Anyway, to load the screensaver, or anything else, you need to add it to your ~/.fluxbox/startup
Any services (e.g. network and volume applets, power manager, etc) you want to run at startup need to be added here.
More info: http://www.fluxbox-wiki.org/index.ph...e_startup_file