Tente isto:
Ligue o seu computador.
Pressione e segure a tecla Shift, o que abrirá o menu do Grub.
Selecione a linha que começa com --- Advanced options
.
Selecione a linha no kernel 3.13 que termina com --- recovery mode
.
O seu PC deve exibir um menu com várias opções.
Selecione network - root
ou netroot
.
Em uma execução de terminal:
# mount -o remount, rw /
# mount --all
# rm -rf /etc/apt/sources.list.d/*.list
# nano /etc/apt/sources.list
No arquivo aberto.
Exclua o conteúdo.
Cole o seguinte:
deb http://us.archive.ubuntu.com/ubuntu/ trusty main restricted
deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates main restricted
deb http://us.archive.ubuntu.com/ubuntu/ trusty universe
deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates universe
deb http://us.archive.ubuntu.com/ubuntu/ trusty multiverse
deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates multiverse
deb http://us.archive.ubuntu.com/ubuntu/ trusty-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu trusty-security main restricted
deb http://security.ubuntu.com/ubuntu trusty-security universe
deb http://security.ubuntu.com/ubuntu trusty-security multiverse
deb http://archive.canonical.com/ubuntu trusty partner
deb http://extras.ubuntu.com/ubuntu trusty main
Ctrl + O Salva o arquivo. Ctrl + X Fechar nano.
E continue em execução:
# dpkg --configure -a
# apt-get -f install
# apt-get -m install
# apt-get update
# apt-get dist-upgrade
# apt-get install --reinstall ubuntu-desktop
# apt-get autoremove
# apt-get clean
# reboot