Nothing is lost. Officially the 7.04 repos are down but unofficially there are still here. They were moved to
Code:
http://old-releases.ubuntu.com/
so you could edit your
sources.list file and change the urls accordingly. To easily edit the file, using for example
gedit, open terminal and do
Code:
gksudo gedit /etc/apt/sources.list
(or just use your favorite editor instead of
gedit)
modily the file and save it
Then do
Code:
sudo apt-get update
and you should be OK. You may even get a notification for updates if you had a long time to update your system.