A webcam black screen usually means the camera is physically blocked, another app has exclusive access, or permissions are wrong. Check for a physical privacy shutter on your laptop or webcam — many newer models have a slider that covers the lens. Close ALL video apps (Zoom, Teams, Meet, FaceTime, OBS, Snap Camera) since most webcams can only be used by one app at a time. Check browser or app permissions for camera access. On Windows, check Settings > Privacy & security > Camera. On Mac, check System Settings > Privacy & Security > Camera. For USB webcams, unplug and replug into a different port. If the camera shows black in every app, the hardware may need a driver reset: on Windows, open Device Manager > Cameras > right-click > Disable device, wait 5 seconds, then Enable device. On Mac, run "sudo killall VDCAssistant" in Terminal.