Your release has reached end of life (EOL), you need to modify /etc/apt/sources.list. Replace CODENAME with the codename of Ubuntu release that you are using.
# Required deb http://old-releases.ubuntu.com/ubuntu/ CODENAME main restricted universe multiverse deb http://old-releases.ubuntu.com/ubuntu/ CODENAME-updates main restricted universe multiverse deb http://old-releases.ubuntu.com/ubuntu/ CODENAME-security main restricted universe multiverse # Optional deb http://old-releases.ubuntu.com/ubuntu/ CODENAME-backports main restricted universe multiverse