You have serious TCP/IP problems but the networking properties dialogue won’t let you uninstall / re-install TCP/IP ?

From Microsoft Support Services:

"When viewing the list of components for a network interface, you may notice that the Uninstall button is disabled when Internet Protocol (TCP/IP) is selected. In Windows XP, the TCP/IP stack is considered a core component of the operating system; therefore, it is not possible to uninstall TCP/IP in Windows XP. In extreme cases, reinstalling the Internet Protocol stack may be the most appropriate solution. With the NetShell utility, you can now reset the TCP/IP stack back to a pristine state, to the same state as when the operating system was installed."

Full instructions