It's an oscilliscope! Much like then one in winamp.
When I play music I get nothing
Make sure you have the recording volume on your sound card turned all the way up. If that doesn’t fix it, make sure you have the latest drivers from nVidia. Failing that try recording something in windows sound recorder. Sound recorder uses roughly the same method of getting audio data from your sound card as bboscilliscope/spectrum, so if it can get sound and the plugins can’t you’ve found a bug
When I don't play music I BBspectrum shows I am
In this case BBspectrum is picking up the static from your sound card. This could mean that you are recording from an analog source, or that you have your microphone un-muted. For best results you should select a fully digital source. I use one called "Wave" on my audigy, but different manufacturers have different names for them. Just try using some different recording lines