Please stop using the Ancient Rome and San Francisco
screensavers you downloaded from this site.
HOW:
Use the right mouse button to click on any "empty" part of
the screen. Do not right-click on any icons.
From the pop-up menu, choose "Properties". If you do not see
Properties listed, try again by right-clicking somewhere else.
The Display Properties dialog box should now be on the screen. Mine looks like this:

Click on the tab marked "Screen Saver".