Computer A has a Windows firewall and B does not. I disabled A's Windows firewall and still B could not ping A. Is it possible that the Norton software (s/w) has installed its own firewall? How do I determine if there's another firewall besides Windows Firewall?
Can you think of any other reasons why, suddenly, after I installed a new modem/router, that previously shared document folders on Computer A cannot be accessed by Computer B?
Let's start with Windows issues. One good article that might help is on Microsoft's support page: How to troubleshoot network in Windows XP. You will also want to check your TCP/IP settings to make sure IP, netmask, and default gateways are all correct.
If those are correct, check to see if you can you ping by IP and/or computer name. Also, check to see of you can see the other computer in Network Neighborhood. If everything looks right here, check the firewall settings.
This was first published in February 2009