Its an well known issue to all types of laptop like HP Dell Lenovo and others. Where you can not find your camera on any messengers. When your camera suddenly disappear from your laptop you will not able ti find it on yahoo messenger, skype, oovoo, Facebook or any other camera related applications because your laptop could not find the webcam.
The solution is so simple and easily :
Step 1: Turn off your laptop (shut down).
Step 2: Now unplug your laptop's power cable.
Step 3: Take your battery off from your laptop for around 10 to 20 seconds.
Step 4: Then attach your battery and turn on your laptop and start using your webcam again.
It is just simple trick that solve your laptop's webcam problem.