Just so I understand you correctly, you have hooked up two monitors to your EVGA 6600 GT. The EVGA 6600 GT has a VGA output, DVI output, and S-Video output. One of the monitors you connected is the Viewsonic VA520 which only has a VGA port. What was the other monitor, does it have a DVI input, and how did you connect it?
Since the video card automatically senses which input the monitor is hooked up to, it may be that the monitor is not returning a signal to the video card. It is rare, but I have seen it happen. Or your video card's DVI port may be bad. Again, it is rare, but not unheard of.