First of all, I just want to say thank you to all of you who have taken time to try to help me out so far.
The tutorial for nView says to start it by connecting a second monitor. I don't have one. Nor does it show up when I right-click the desktop.
I don't think it is a hardware issue - I had it working well for a while under the older drivers (although that doesn't seem to be the case anymore), and it works perfectly fine under Linux. So it must be some sort of software conflict or bug.