What kind of internet connection do you have? eg cable, DSL
Do you have a router?
Is your connection working correctly with other systems?
Regardless of whether there is a router, is the connection to the computer set up for a fixed (static) IP address or for DHCP (dynamic IP)
Please provide as much detail as possible about the configuration.
Also, open a terminal, and enter:
ping
www.google.com
If there is no response, then try (numeric IP for Google):
ping 74.125.19.99
If this version works, then you simply need to enter you DNS host information into the network configuration.