Not quite sure how cable routers work, in the sense of what network services they do, but I can give you some rough stuff to check:
Can any machines access the FTP/HTTP servers? If not (or only the machine it's running on) then it's probably the firewall on that machine.
Since you're running two routers, you should have DHCP disabled on the one that's not connected to the internet (I know with a DSL connection, you have the gateway router doing DHCP unless you can configure the settings fully so that the gateway points to the router providing internet).
If you've had to change that, then you'll need to restart the secondary router (and renew IP addresses on all machines on the network) to get the single DHCP pool working.
If either of those don't do anything, prod me on steam or IRC and I'll see what else I can try for you