What errors are seen in /var/log/Xorg.0.log file?
Check /var/log/dpkg.log for a trace of what was installed previously
and what was removed and what was recently installed.
I think it
likely your xserver driver was removed due to a conflict. Figure out
what had been running and install it again.
If the current Testing no longer contains the right combination of
packages for your xserver then look up the previous version of the
packages on http://snapshot.debian.org/ where all package versions are
archived. You can undo the recent installation and downgrade revert
to the previous packages from there.
> I can boot in recovery mode but if I do that as root if I run aptitude it
> doesn't download packages - I think there is no internet connection being
> made.
That makes me think you are running NetworkManager. By default it
seems to want the desktop user to start networking.
Try using the network manage command line client to start networking.
I can't suggest a command as I am not running NetworkManager (due to
problems such as these) and therefore don't know the command line to
suggest. Others may be able to help better.
Bob