If you installed server then you probably do not have a GUI. You need to edit the sources.list file.
At the top comment out the CD-rom and uncomment main, universe and the multiverse repositories. If you are unsure about what to comment out then post the file.
sudo nano /etc/apt/sources.list
Then you need to update apt.
Pinging is a good method to test your internet connection. You might have a DNS issue. Try pinging by domain name and ip address. 126.96.36.199 is a good address to ping. If the name does not work then it is a DNS issue.
sudo apt-get update