Built-in iSight camera in MacBook Pro stops working in Skype
I've seen problems like this before with Skype and I'm pretty sure there's nothing you can do about it.  Make sure you're not running any other apps that are using the camera and that you've got the latest version of Skype installed.  I've found that sometimes going into the Skype preferences and clicking on the "Audio/Video" icon can "free" it up.