Your network settings or your Windows installation aren’t good.
For network, you can try WinSock Fix (http://www.majorgeeks.com/WinSock_XP_Fix_d4372.html).
Use Reg-Backup button before fixing.
For Windows installation, overinstallation can solve the problem and you won’t lose your programs, settings, data, files, etc. Just choose ‘Repair’ installation of Windows and install ‘over’ the old installation.
http://support.microsoft.com/default.aspx?scid=kb;EN-US;315341
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q314058
http://www.webtree.ca/windowsxp/repair_xp.htm