Most camera issues can be due to a physical privacy cover covering the lens. Make sure that's not the case.
Otherwise there is usually a physical button/key/switch you can use to turn the camera on or off. For example, most Lenovo uses F8 or Fn+F8, or a switch above the lens, HP has a camera key or a button on the side of the laptop, MSI uses F6 or Fn+F6, etc.
If you are not sure or cannot find it, tell me the brand and model so I can find out where specifically to press/open, etc.