Update=Resolved-RESOLVED!! I switched the monitor connections and the mouse now freely moves between screens.
I have a new Dell XPS 8940 desktop. I have two older Dell monitors, specifically Model 1901FP. I have one connected to the desktop and want to add a 2nd monitor as I work dual monitor.  The 1901FP has the following ports: VGA, USB, DVI. The one I have successfully set up is connected via VGA to HDMI adapter. My tech store advised that I purchase a DisplayPort adapter, DisplayPort (20 pin) Male, VGA Active Adapter (VGA (15 pin; High Density D-Sub) Female. I plugged the 2nd monitor into the adapter, then plugged the adapter into the Display Port. I cannot make the 2nd monitor work. Help please.
XPS 8940 add second monitor, DisplayPort to VGA cable