Additional features, settings, or issues not covered by specific Microsoft Teams Free categories
1
Open the Camera app in Windows, is your webcam working in that app.
2
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.
3
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?