I've run into this several times and get stumped each time. either because of malware or corrupt files or settings, I have a win xp pc that can't file share. I think I've covered all the bases. it comes down to needing to turn off the firewall... but the windows firewall is already off / has an exception for file sharing, etc....
I've run winsockxpfix loads of times to repair web connections (I can ping websites, they resolve the ip at a dos line, but nothing will come up in the browser till you run winsockxpfix).
Is there an app or where would I look in the registry to clean out firewall settings. sometimes I will install zone alarm then uninstall it and that clears out the corruption / the pc can share files successfully. But that isn't a sure thing. on this machine, that is not working and i need to share a folder.