Screen Saver does not activate after time expires

I have never been able to get my screen savers to activate after time has expired. Any Ideas how to correct this? I am running McAfee VS. The only way I can activate my screen saver is to double click on McAfee ScreenScan. I have removed the check mark next to Enable screening while in the Screen saver mode and it still does not activate after the time has expired. Can anyone help?