My MacBook Pro 2011(Lion OS) won't download anything, it starts and just completes at about 200kb no matter how large the download is and it also doesn't stream anything on YouTube or any video site, it starts buffering then stops after about a second or two BUT when I'm downloading a torrent file it completes it perfectly and its not my connection cos I've tried two different networks and also I've tried my connection on my sisters PC and everything works perfectly there, what could be the problem?