1.Try to use WinSock XP Fix 1.2 which fixes the winsock settings on your Windows XP machine. This tool is recommended for IT professionals only.
It can often cure the problem of lost connections after the removal of Adware components or improper uninstall of firewall applications or other tools that modify the XP network and Winsock settings.
If you encounter connection problems after removing network related software, Adware or after registry clean-up and all other ways fail, then give WinSock XP Fix a try.

2.Reset Internet Protocol (TCP/IP) in Windows XP. You can find information on how to do that here: http://support.microsoft.com/?id=299357

3. One possible answer involves a bug in Service Pack 2 of Windows XP dealing with a loss of network connectivity for workstations that use Microsoftâ€@trade;s L2TP-based virtual private networking (VPN) client to connect to servers that are connected to NAT-based networks. However, this bug seems to appear in situations that are not associated with VPNs either.

If patching Windows XP for this bug does not fix the problem, you may have to reinstall your firewall, rebuild the configuration in your router, or assign static IP addresses to your computer to resolve this issue.

4. Your Network or DSL router may have bad or missing information. Powercycle your router and/or rebuild the configuration in your router.

5. Check your network card to make sure its configured correctly and working properly. Many times setting the network card to 10Mbps/Full Duplex will solve this issue. To do this, open Control Panel, System, Device Manager. Go to the properties of the Network card, click on the Advanced tab and find the Link Speed and Duplex section. Change it from Auto Detect to 10Mbps/Full Duplex.

6. Check and test your firewall. Your firewall, especially if its a software firewall like ZoneAlarm, Black Ice, Norton Firewall or something else could be blocking the connection. Disable your firewall and test the connection. You may have to resolve the problem by even uninstalling and reinstalling the firewall.

7. Check your IP address assignments and workgroup settings in the computer for accuracy. Statically assign an IP to the computer.