1
Look at the function keys (F1 - F12) on your keyboard, if one of them has a camera icon, press that key or Fn + that key to unlock the webcam.
2
If that was not the problem, look at the camera lens above your screen, is there a small privacy slider that needs to be opened to access the webcam?
3
If the webcam is still not working:
Right click your Start Button and open Device manager.
Expand the Cameras section.
Please provide a screenshot of that full device Manager window.