USB to VGA multidisplay adapter

[dee227]

I have a Macbook Pro (OSX 10.6.8) and have connected through its mini DVI port to a projector. I bought a USB to VGA adapter to add another monitor but that monitor doesn't display what I have on the computer screen (just black). I'm trying to use it with programs like Keynote...
Any suggestions?
Lisa

 

[MindoverMaster]

I'm not well versed with OSX, but is there a setting for monitors? Try looking in there. Might have to manually enable it.