Go ahead and open terminal/console for your server.
Edit this file using your favorite editor.
sudo nano /etc/network/interfaces
This is how it looks (using DHCP)
auto eth0
iface eth0 inet dhcp
Now, some editing required. Change it to this :
auto eth0
iface eth0 inet static
address 192.168.1.100
netmask 255.255.255.0
network 192.168.1.0
broadcast 192.168.1.255
gateway 192.168.1.1
Save it. Next we need to change some parameters in /etc/resolv.conf
sudo nano /etc/resolv.conf
Change the line 'nameserver xx.xx.xx.xx' to 'nameserver 192.168.1.4' where 192.168.1.4 is your name server.
Now, remove dhcp-client from your server.
sudo apt-get remove dhcp-client
Lastly, we need to restart networking service
sudo /etc/init.d/networking restart
Done. Try and ping any server (yahoo, google etc).
