Boas!
sudo cp /etc/apt/sources.list /etc/apt/sources.list_baksudo gedit /etc/apt/sources.listApaga tudo uk lá tens e mete isto:
#-------------------------------------------------------------------------------------------------------------------
## Add comments (##) in front of any line to remove it from being checked.
## Use the following sources.list at your own risk.
deb
ftp://pt.archive.ubuntu.com/ubuntu dapper main restricted universe multiverse
deb-src
ftp://pt.archive.ubuntu.com/ubuntu dapper main restricted universe multiverse
## MAJOR BUG FIX UPDATES produced after the final release
deb
ftp://pt.archive.ubuntu.com/ubuntu dapper-updates main restricted universe multiverse
deb-src
ftp://pt.archive.ubuntu.com/ubuntu dapper-updates main restricted universe multiverse
## UBUNTU SECURITY UPDATES
deb
ftp://pt.archive.ubuntu.com/ubuntu dapper-security main restricted universe multiverse
deb-src
ftp://pt.archive.ubuntu.com/ubuntu dapper-security main restricted universe multiverse
## BACKPORTS REPOSITORY (Unsupported. May contain illegal packages. Use at own risk.)
deb
ftp://pt.archive.ubuntu.com/ubuntu dapper-backports main restricted universe multiverse
deb-src
ftp://pt.archive.ubuntu.com/ubuntu dapper-backports main restricted universe multiverse
#-------------------------------------------------------------------------------------------------------------------
Grava, vai a uma shell e faz:
sudo apt-get updateE pronto, ficas com isso pronto...
sLUGo @ Portugal