HOWTO:

Restore Internet and Network Connectivity

1. Try releasing the IP address configuration and renewing it.  To do this, click Start -> Run -> type in cmd into the dialog box and click Okay.  Next type in ipconfig /release and hit enter.  The command should then say network configuration released.  Finally type in ipconfig /renew and hit enter.  This should send a DHCP request from your computer to get the network address configuration.
2. If you cannot ping using the name of a web site, but can ping via IP address, the DNS cache might need to be flushed. To do this, click Start -> Run -> type in cmd into the dialog box and click Okay.  Next type in ipconfig /flushdns and hit enter.  The command should say successfully flushed the DNS cache.  Try using ping and the name of a web site and it should work now.
3. If that still does not work, the TCP/IP protocol might be corrupted.  To fix this, click Start -> Run -> type in cmd into the dialog box and click Okay.  Next type in netsh interface ip reset c:\resetlog.txt and hit enter.  The command should reset the TCP/IP stack to default settings.  Reboot your computer after running this command, and you should have network connectivity.
4. One last troubleshooting step you can try is to reset the Winsock stack.  To fix this, click Start -> Run -> type in cmd into the dialog box and click Okay.  Next type in netsh winsock reset and hit enter.  This command should reset the Winsock stack to default settings.  Reboot your computer after running this command, and you should have network connectivity.