how about this:
W: Failed to fetch http://ppa.launchpad.net/backbox-desktop/gnome3-builds/ubuntu/dists/natty/main/source/Sources 404 Not Found
W: Failed to fetch http://ppa.launchpad.net/backbox-desktop/gnome3-builds/ubuntu/dists/natty/main/binary-amd64/Packages 404 Not Found
W: Failed to fetch http://ppa.launchpad.net/backbox-ppa/backports/ubuntu/dists/natty/main/source/Sources 404 Not Found
W: Failed to fetch http://ppa.launchpad.net/backbox-ppa/backports/ubuntu/dists/natty/main/binary-amd64/Packages 404 Not Found
W: Failed to fetch http://ppa.launchpad.net/ubuntu-desktop/gnome3-builds/ubuntu/dists/natty/main/source/Sources 404 Not Found
W: Failed to fetch http://ppa.launchpad.net/ubuntu-desktop/gnome3-builds/ubuntu/dists/natty/main/binary-amd64/Packages 404 Not Found
can you give an explanation to me, sorry im newbie.