I think the problem you're having is that the All-in-one isn't getting an IP address. Typically you can only get one IP address from a cable modem at a time, and mine is such that if you change the device that is attached to the modem, you have to reset the modem (I think it's based on MAC address).
What that means is, when you're trying to get the network subsystem up and running on the all-in-one, it goes out, looks for an IP address using DHCP, but can't get one, so it defaults to an auto-config address. In order to get things working properly, I would suggest you buy a router and replace the switch with it (assuming the router has a built-in switch). It will get an IP address from your cable modem and then distribute private addresses to the computers on your network.