ps de igual forma no me bajan algunas actualizaciones con el gestor, me dice que no se problema hay con el servidor 
hmmm talvez tocaste sin querer los archivos donde estan los repositorios de ubunutu, ese esta en /etc/apt/sources.lst
aqui te dejo el mio, es para el ultimo ubuntu asi que ojo, y para editarlo no te olvides de hacerlo como root o usar sudo
#deb cdrom:[Ubuntu 8.04.1 _Hardy Heron_ - Release amd64 (20080702.1)]/ hardy main restricted
# See
http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb
http://gt.archive.ubuntu.com/ubuntu/ hardy main restricted
deb-src
http://gt.archive.ubuntu.com/ubuntu/ hardy main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb
http://gt.archive.ubuntu.com/ubuntu/ hardy-updates main restricted
deb-src
http://gt.archive.ubuntu.com/ubuntu/ hardy-updates main restricted
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## universe WILL NOT receive any review or updates from the Ubuntu security
## team.
deb
http://gt.archive.ubuntu.com/ubuntu/ hardy universe
deb-src
http://gt.archive.ubuntu.com/ubuntu/ hardy universe
deb
http://gt.archive.ubuntu.com/ubuntu/ hardy-updates universe
deb-src
http://gt.archive.ubuntu.com/ubuntu/ hardy-updates universe
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb
http://gt.archive.ubuntu.com/ubuntu/ hardy multiverse
deb-src
http://gt.archive.ubuntu.com/ubuntu/ hardy multiverse
deb
http://gt.archive.ubuntu.com/ubuntu/ hardy-updates multiverse
deb-src
http://gt.archive.ubuntu.com/ubuntu/ hardy-updates multiverse
## Uncomment the following two lines to add software from the 'backports'
## repository.
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
# deb
http://gt.archive.ubuntu.com/ubuntu/ hardy-backports main restricted universe multiverse
# deb-src
http://gt.archive.ubuntu.com/ubuntu/ hardy-backports main restricted universe multiverse
## Uncomment the following two lines to add software from Canonical's
## 'partner' repository. This software is not part of Ubuntu, but is
## offered by Canonical and the respective vendors as a service to Ubuntu
## users.
# deb
http://archive.canonical.com/ubuntu hardy partner
# deb-src
http://archive.canonical.com/ubuntu hardy partner
deb
http://security.ubuntu.com/ubuntu hardy-security main restricted
deb-src
http://security.ubuntu.com/ubuntu hardy-security main restricted
deb
http://security.ubuntu.com/ubuntu hardy-security universe
deb-src
http://security.ubuntu.com/ubuntu hardy-security universe
deb
http://security.ubuntu.com/ubuntu hardy-security multiverse
deb-src
http://security.ubuntu.com/ubuntu hardy-security multiverse
