Often you'll not find anything obviously wrong in Network Neighborhood or with the ping command. What can be done? On Windows XP, fortunately there is a simple fix that works in many cases.
> WinSock Fix for Windows XP Network Clients

Recover from Network Corruption in Windows XP
In Windows networking, corruption of the WinSock installation can cause network connections to fail on computers running Windows XP (and other Windows operating systems). This corruption sometimes occurs when you uninstall software applications that rely on WinSock. These applications include adware / spyware systems, software firewalls, and other Internet-aware programs.

To fix WinSock corruption problems, follow either of the two methods described below.
Fix WinSock2 Corruption - Microsoft
For Windows XP and Windows 2003 Server systems, Microsoft recommends following a specific manual procedure to recover from WinSock network issues caused by corruption. The procedure varies depending on whether you have Windows XP Service Pack 2 (SP2) installed.

With XP SP2, the 'netsh' administrative command-line program can repair WinSock.

For older Windows XP installations without XP SP2 installed, the procedure requires two steps:

* modifying the related Windows Registry keys
* re-installing the TCP/IP protocol
More


WinSock XP Fix - Freeware
If you find Microsoft's directions too cumbersome, an alternative exists.
Several Internet sites offer a free utility called WinSock XP Fix. This utility offers an automated way to repair the WinSock settings. This utility runs only on Windows XP, not on Windows Server 2003.

Download - WinSock XP Fix 1.2