Why is it that only two of the three computers on my home network can acsess files from each other?

I have three computers connected to an ethernet switch, an older custom built that was upgraded to XP Pro from Win 98, a Compaq Presario 6400NX with XP Home, and a 2006 HP Pavilon with XP pro.

Only the custom built and the compaq can accsess each other's files although all three of them can acsess the internet through the sbc yahoo dsl homeportal 1100.

I am sure that I have all the folders that need to be shared selected to shared.

I am sure that all firewalls allow file sharing.

So my question is, if the internet works on the hp, then why doesn't file sharing?

Why is it that only two of the three computers on my home network can acsess files from each other?systemworks

for each to inter-access all other compr's they all must have the file sharing enabled, have the same user group name and passwords.