These articles can be more useful once printed, because if you encounter this problem, you won't have access to this page!
Several factors can prevent the internet connection to work correctly. Here is what you can try in priority order :
Restart the modem and router (soon)
Enable the wireless network on a laptop (soon)
Enable network connections (soon)
Repair Winsock on Windows (soon)
If none of this works, the last option is to call your Internet service provider to see if there is a network problem at the moment or to solicit their support.