Is port 4 shared with the uplink port on the router? If so, is the uplink port populated? If the answer is yes in both cases, port 4 won't work.
Is your switch one where the uplink port is switchable between uplink and standard? If so, did you make sure it's set to uplink? Also, make sure you're not using whatever port is shared with the uplink.
Are you using the DHCP feature of the router? If so, are the additional systems set to aquire an IP address automatically, and did you reboot them after hooking them up?
Russ, NCNE