banhien has given you the official answer link and all the help that is available for this. It is really the best help.
I will fill in the extra for you and try to help you understand some of the extra bits:
These next statements true to the extent of the explanation that follows:
The Device Manager is in charge of the hardware on your notebook. The Device Manager keeps track of the devices and provides a way for you to see the connection points.
The Device Manager can only "see" the devices that are connected to it: keyboards, USB devices (flash drives, etc), fingerprinters (if you have one), and ... webcams.
If, suddenly, something happens and the Device manage looses track of a device for ANY reason, it cannot "see" it any longer. For all intents and purposes, the device (your webcam) no longer exists. As far as the Device Manger is concerned, the device is gone, so it says, "No such device detected".
What can go wrong?
Most common failures include:
Electronic failures - lost signals, driver failures, weird little lost instruction package errors
Hardware failures - sudden electronic or physical failures in a particular device
In particular, with Webcams: broken or loose wires, crushed wires, or something similar that results in the same thing: a disconnect from the physical camera that is built in to the notebook.
If you go through ALL the suggested fixes for your webcam, including a Hard Reset of the notebook (which might work!), then it is time to consider that MAYBE you have a hardware issue. It is not uncommon for webcams to break - they are fragile. Webcams are not usually terribly hard to fix (lots of YouTube howto videos out there), or you can send/take it in to a shop.