Run it in termial and see if there is a error while running the program.

I have fFuxbox installed and it works fine in both 7.10 and 8.04. Did you
install it properly? Try to re-install it. Also make sure you have fluxbox,
fbpager and fluxconf. The menus are included in fluxconf, I believe. If all else
fails Ctrl-Alt-backspace will get you out of X.

I think that you may have found the fly in my ointment. I
downloaded fluxbox and fluxconf, but I don't remember fbpager in the
mix.