Brainstorm uses your browsers built in handler to devices connected to your PC/Mac. If you can not see your video or the audio feedback green indicator in the troubleshoot dialog then chances are your default Camera and Microphone are not setup properly. In such an event please select a new cam/microphone device or connect an external mic/cam like a USB webcam and mic or analog mic (if your machine has a mic in jack) and try selecting this new device from the audio device list.
The device selector dialog can be accessed from the Troubleshoot dialog by clicking the button labelled "change microphone and/or cam".
Alternatively click the A/V setup button in the Brainstorm UI to bring up the devices list dialog