you likely have an /etc/X11/xorg.conf that is configured to use a propriatory driver that was not upgraded when you did the upgrade to Jessie. This is would be why you are not gettting a gui now. If you are using networkmanager to configure your network, then I think the network will not be configured unless you start the graphical environment.
So to get the graphical environment and hence the network back you should try to use the free graphics driver that your system already has. This may be as simple as moving your config file out of the way. Eg as root
mv /etc/X11/xorg.conf /etc/X11/xorg.conf.save
And then trying to restart X (or just reboot).
PS. There are lots of useful diagnostics information that would help in understanding the underlying problem (log files hardware listings etc), but since you don't have a gui or network you may struggle to provide this information. This is why I've suggested the approach above.