Cheese just doesn't detect the webcam .. nor other software. This is an MSI GT70 2PC. I cannot even find someone having the problem. The webcam even works fine on windows 8.1 .
I also tried adding the user to the video group and I even tried this:
sudo chmod 777 /dev/video*
following this question but ubuntu can't find the directory in the first place!
Maybe the camera is locked. I own a MSI GS70-2PC-210US and from time to time this happens to me after doing updates.
Try pressing Fn+F6 (or whatever the camera lock/unlock button is located on your keyboard).
Try going on "additional drivers" (you can search for it on the Ubuntu search engine) and looking for any proprietary drivers for your device. It usually works for me.