It sounds like the built-in webcam has failed to the extent that Windows can no longer detect it - - effectively it doesn't exist.
However, just to make sure, open Device Manager too see if the webcam is listed under "Imaging devices". If it isn't, and if there are no "unknown device" errors (question mark) or other error icons in there, the webcam has definitely failed.
You can buy an external webcam which plugs in to a USB port on your laptop, and some of them can be clipped to the top of the screen so it's roughly in the same position as the internal one.