I've recently started to use Ubuntu 12.10. My camera was working fine for the last three weeks but now it shows me a black picture.
Hope you can help me as soon as possible.
There is a problem with some filters installed that are not working properly and the webcam is not configured properly. Open a terminal window and log in with root access then use gstreamer-properties to configure the webcam. Also, don't try to install the default drivers for the webcam because most of the times these drivers are in beta stage and they don't work at all with the intended product.