Well, what exactly have you tried to get it working? I assume this is Ethernet, and not WiFi?
You first want to be sure that your NIC is properly detected. You can verify this by running "ifconfig" without any parameters. You should see two interfaces at the very least, "lo" and "eth0". If you only have "lo", then there is a problem and you will need to give us more information.
If you have an eth0, then doing something like the following would get a DHCP lease:
sudo dhcpcd -t 30 eth0
Does that not work?