sudo apt-get install aptitude
sudo aptitude show ssh
to see if the openssh-server is installed (on our new PCs it wasn't after installing Ubuntu)
sudo aptitude install openssh-server
ifconfig and check if the IP address in the eth0 connection is the same as in the IPv4 setting in the gui (it wasn't in the case of the new PCs)
Enable networking by right-clicking on the network icon at the top of the desktop.
Restart network manager
sudo service network-manager restart
Now, the IP from ifconfig and from the IPv4 settings should be the same and ssh should work.