Can't stop mirroring in dual monitor setup

I am running Ubuntu 14.04.3 64-bit, and have two Dell 17" monitors connected at a single VGA port. Both monitors are on, and mirror the same display. I am not able to detect the second monitor, when running "Detect Displays". Here's the output of xrandr -q

Screen 0: minimum 320 x 200, current 1280 x 1024, maximum 8192 x 8192
DVI-I-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 disconnected (normal left inverted right x axis y axis)
VGA-1 connected primary 1280x1024+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
   1280x1024      60.0*+   75.0  
   1152x864       75.0  
   1024x768       75.1     60.0  
   800x600        75.0     60.3     56.2  

   848x480        60.0  
   640x480        75.0     60.0     59.9  
   720x400        70.1  

I tried disconnecting one monitor. This changes the detected display from "Unknown" to "Dell 17". I also tried connecting the second monitor at the DVI port, but that alters my primary monitor display, I lose the mouse, and have no way to operate properly. What hardware setup is ideal for dual monitors? How do I solve this problem? I appreciate your feedback.

Thanks,
Anjy