isight issue

So I recently bought a refurbished macbook pro off apple and for some reason the isight camera is not working efficiently. Whenever I'm video chatting with my friends on ichat, the video window just automatically shuts off. Whenever I use photo booth the camera keeps shutting on and off giving me a message camera is not connected. I went to the apple store and they replaced my camera but still this issue keeps happening. I did an archival install of osx and nothing helped. I whipped the hard drive and did an install of osx and that still didnt help. What should I do!!