Most Internet connectivity problems arise out of corrupt Winsock settings due to the installation of a networking software or Malware infestation.
If your using Windows XP SP2, log on as an administrator.
Go to Start > Run and type: cmd
Press OK or Hit Enter. A dos Window will appear.
At the command prompt, type or copy/paste: netsh winsock reset
When the program is finished, you will receive the message: "Successfully reset the Winsock Catalog. You must restart the machine in order to complete the reset
Close the command box and reboot your computer.
Go to Start > Run > type: cmd
Press OK or Hit Enter.
At the command prompt, type or copy/paste: ipconfig /flushdns
Close the command box.
Then go to Start > Control Panel, and choose Network Connections
Right click on your default connection, usually Local Area Connection or Dial-up Connection if you are using Dial-up, and and choose Properties.
Double-click on the Internet Protocol (TCP/IP) item.
Select the radio button that says "Obtain DNS servers automatically
Click OK twice to get out of the properties screen and restart your computer.
If you continue to connectivity problems, download and run WinSockFix
.Be sure to print out and follow the instructions provided in the Winsock Repair Tutorial.