What device are you using Teams on, is that a Windows PC?
1
In Teams, there is a switch for enabling the webcam, is that turned on?
2
If you are using Teams on a Windows device, open the Camera app, is the webcam working in that app?
If not:
A
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.
B
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?