Just a few more details might help. Are you connecting to your router wirelessly or via a cable? Or do you use a modem rather than a router to connect to the Internet? Is networking working on your PC and it is just the Internet that doesn't work or is networking not working at all? Have you been through the network troubleshooting wizard?
Give us details of your equipment and state exactly what is, or isn't, happening and someone may be able to advise you further.