If you can't see the second monitor in control panel and you know the monitor is working, then the 650 isn't functioning correctly or you have something wrong between the 650 and the monitor.
I have a machine with a 650 in it and it only has 2xDVI ports and a mini-HDMI. Are these the available ports on the back of yours?
If yes, are you saying you're using a DVI to VGA converter? If so, the converter or the cable might be the issue.