Open /etc/apt/sources.list file, find and uncomment the following lines
deb http://us.archive.ubuntu.com/ubuntu dapper universe main restricted universe
deb http://security.ubuntu.com/ubuntu dapper-security universe
sudo apt-get update
Open /etc/apt/sources.list file, find and uncomment the following lines
deb http://us.archive.ubuntu.com/ubuntu dapper universe main restricted universe
deb http://security.ubuntu.com/ubuntu dapper-security universe
sudo apt-get update