screensaver issues / resume/ log-on

So I'm trying to fix the issue of bringing up the log-on screen
after being away from the computer ( on resume )

However before I do that, the screensaver must work
Which it doesn't , and I can't figure out why not?

The previews are fine. I wonder what idle really means?
Do I have something running in the background which
windows thinks means activity. Any ideas peeps?

bump
It works now since I disabled a download called classic shell win 7

I have not used a Screensaver in years.

Gary its more to do with research for a problem at work
whereby peeps leave their desks and maybe leave station logged on
I need a simple workaround e.g screensaver kicks in
and brings up the log-on screen = problem solved ..