Solution 1: Check the recorder control bar to make sure the webcam feature is turned on.
Solution 2: If you are using an external webcam, make sure it is properly connected to your computer (typically they plug in via a USB port).
Solution 3: Ensure you've installed the latest software for the webcam. If your webcam is built-in to your laptop, you can get the drivers from your laptop manufacturer's support site.
Logitech c920 is one of the most popular - unplugging the camera, re-installing the drivers, re-connecting the camera and re-opening VidGrid will fix the issue.
Download latest drivers here: https://support.logitech.com/en_us/product/hd-pro-webcam-c920/downloads