It helps if you identify your computer model and webcam, and whether it is built in or add-on, and if add-on, mfg & Model number.
Here is a fix for HP, for example. The same tact may work for you, although the driver names may not be the same.
here is the solution that I found out after 4 months of facing the same
problem and no response or help from countless contacts with the HP
Simplo webcam update from 'Microsoft windows update' was installed
this update messed up the webcam entry in device manager by removing the imaging device from the list and there is no way to uninstall this
Here is the solution:
-open device manager
-expand usb controllers list
-select 'Simplo webcam' device and press uninstall. Check box 'Also
-press the button 'detect hardware changes'. A new imaging device will
appear as 'Ricoh webcam. Repeat previous steps for this device in order
to delete it as well. Press again the button 'detect hardware changes'.
The correct device 'HP Webcam' will appear in the list. Webcam is now
ready for use.