We have Windows XP Pro and XP Home and windows 2000. When We First Installed Our Router The 2 XP's file sharing worked. we have a Linksys router. After a while our File Sharing went completly away How do I configure my network configurations on these computers to make them all see each other

Make sure all PC's are in the same workgroup, on the same ip subnet, are pingable via their hostname, and file sharing is allowed through the firewall on each pc.