I installed Ubuntu server 14.03 in a Virtual Machine and after installation the Internet connection was not working. To fix this I added the nameservers to the /etc/resolv.conf file like this.
nameserver 126.96.36.199 nameserver 188.8.131.52
After saving this file, I ran this command.
sudo service resolveconf restart
This fixed the issue with the Internet connection in the Ubuntu server VM. This was an easy fix and allowed me to run
sudo apt-get update and then
sudo apt-get upgrade to update the installed system. And this persisted after a shutdown and startup. So this is what I recommend you try if you are also having issues with networking in Ubuntu server. It worked for me.