Are the firewalls configured properly? Did you try what LEN said or did you turn on DHCP in the switch? I can think of so many potential problems, since I've had such problems in our family network here numerous times. if you set static IPs, that will also allow you to try to ping the other computer, if that works, you should control firewall settings and whether windows is set to give file access etc.Without giving file access to other computers, they may not show up at all in your network.