If this happens to your camera, simply unplug the camera and plug it back in. A simple power cycle should bring the camera back online and it will pull up in ViperVision.
Make a note of how the camera cut out. Is it a new camera? Did you shut down the software and open it back up and the camera was not available? If the camera fell out on its own, refer to the Trouble connecting a camera section of the troubleshooting guide.