Lots of modern laptops have a pyhsical shutter for built-in webcams, which can be used to disable your camera for privacy.

If the shutter is closed it will stop your webcam from working and you may see error messages to this effect in Windows.

If you find your camera is not working, please try finding your shutter and sliding it across to check that the shutter is not blocking the camera. On some laptops there may a button instead (usually with a camera icon) of a sliding switch/toggle.

Some visual examples to help you find your shutter: