My computer doesn't seem to be able to connect with the isight camera (I have a 2008 macbook pro). Whenever I shut the computer down, I am able to use the isight camera on ichat, but after a day (a couple of hours), the videochat icon switches to an audio chat icon and I don't seem to be able to access the ichat camera in any of my applications (facebook, etc). What is causing this and how can I ensure that this won't happen?