small network is all fouled up ...
 

I have two routers and a cable modem with several computers. However, the
machine colocated with the cable modem can't "see" the ones downstream,
though they can "see" (at least PING) it. I thought I set up the network
identically on each machine but don't even have a network access icon in the
taskbar on that one machine.

None of the machines "see" each other in Network Neighborhood, nor do they
"see" what's in their workgroup. They have, of course, been assigned to the
same workgroup.

What's going on here?