At times it is necessary to repair TCP/IP stack because the links between the layers may become broken. When you try pinging an address, you get a response but still cannot connect to your network or the internet.
Start > All Programs > Accessories and right click on "Command Prompt", select "Run as Administrator" to open a command prompt. In the command prompt window that opens, type type the following commands, each followed by the Enter key:
Reboot the machine.
For Windows XP, right click on the Command Prompt and type netsh int ip reset