Privacy check first
Settings → Privacy → Camera → Allow apps to access your camera: On. Scroll down and confirm the specific app (Teams, Zoom, Chrome) is allowed.
Device Manager
Device Manager → Cameras (or Imaging Devices). If the webcam shows a yellow exclamation: right-click → Update driver → Search automatically. If no webcam appears at all, check Universal Serial Bus controllers for unknown devices.
Driver reinstall
Right-click the webcam → Uninstall device → check "Delete the driver" → reboot. Windows reinstalls the default driver. For OEM built-in cameras, download the specific driver from the laptop manufacturer's support page.
App-specific fix
If the webcam works in one app but not another: in the failing app, go to Settings → Video/Camera and explicitly select the camera device — it may be set to a virtual camera or the wrong device.
USB webcam hardware test
Test on another computer. Try a different USB port. USB 3.0 ports (blue) sometimes interfere with older webcam chipsets — try a USB 2.0 port instead.