If the firewall is enabled and you don't have File & Print Sharing enabled in the firewall settings ping requests will be dropped.
Show firewall configuration:
C:\Documents and Settings\Admin>netsh
The VPN entry at the end of your firewall configuration dump.
If you are running any type of VPN client, ie. like from Cisco, openvpn, etc... sometimes those include a built-in firewall function that can cause issues like blocking incomng Remote Desktop requests for example.
Subnetmask doens't care in this situation. Also subnetmask is not a problem.
You can use 194.x.y.z as B Class with 255.255.0.0.The problem is TCP\IP. If you can't ping localhost, TCP\IP isn't working properly so never can ping ther machines.
reset your TCP/IP configuration. It is not working properly.
To reset TCP\IP in Windows XP
Disable Norton Internet Security firewall