There have been occasional reports whereby the removal of certain
malware can cause the loss of all connections to the Internet.
Fortunately this event is fairly rare, but what the malware has done
is to insert a piece of software called an LSP (Layered Service Provider)
into the Windows TCP/IP handler.
It is known that using Adaware 6 to remove this type of malware on
an XP machine, or manually deleting the LSP.dll can subsequently damage
the TCP/IP protocol.
Because TCP/IP is built into Windows XP, it cannot be removed or
re-installed (as you could in previous versions of Windows) and as
such you would have to re-install XP to fix this problem.
Microsoft have since issued two articles which may help in these
~ How to reset Internet Protocol (TCP/IP) in Windows XP.
~ How to determine and recover from Winsock2 corruption.
A simpler solution may to to try either:-
a free utility from cexx.org
XP Fix freeware by Option Explicit (which is also said to work
in Windows 2000).
"LSP-Fix repairs Winsock 2 settings, caused by buggy or
improperly-removed Internet software, that result in loss of Internet
"WinSock XP Fix offers a last resort if your Internet connectivity
has been corrupted due to invalid or removed registry entries."