An external webcam might not be recognized due to several reasons, such as connection issues, outdated or missing drivers, or conflicts with other USB devices. Firstly, ensure the webcam is correctly connected to a functional USB port. Try different ports to rule out a port issue. If the webcam is not recognized after that, open Device Manager and look for any devices marked with a yellow exclamation point, indicating a driver issue. Updating the USB controllers and webcam drivers through Device Manager can help. If problems persist, try the webcam on another computer to see if the issue lies with the webcam itself.