I'm trying to install qmail in debian. I'm not a debian guy but its the OS of the server so I have no choice. It needs high version of perl so I'm installing it via .deb but its looking a lot of dependencies. Then I tried to use apt-get. I first command "apt-get update" then "apt-get -f install". It tooks some time before it finish though sometimes I cancel it then run the command again. Suddenly, when I tried to vi some files, nothing happens. Even the less commands are not working. Is there someone could point me how to restore back?

Be glad, the PROPER choice has been made for you

Now, you seem to have worked quite .. disorganized .. who knows in what ways you fscked up your system. When you say that "nothing happens" do you mean your session goes something like this:

with vi never appearing? I guess your best chance is a reinstall but never the less.. try an apt-get update, an apt-get -f install, let them run, why did you keep interrupting them? see the manual page for enabling some extra verbosity delicousness.