I know this is a trivial question, but it's been annoying me and googling 
hasn't helped.

I'm running Debian Testing, KDE 3.5.  The setting in KDE's Control Center 
doesn't seem to apply.  All I get for a screen blank is the large X.  

I'm guessing this is from either Xorg or kdm (my login manger), but I don't 
know how to get it out of the way to let my KDE setting work.

Any pointers appreciated.

Mark Mitchell