No comunication between router and cable modem.

this is because your PC is picking up the WRTG54G which is an internal signal booster (internal gateway) to the ROUTER ITSELF.
WRTG54G is in the middle like an interpreter.
The WRTG54G is not connect to ROUTER>
thus the laptop is not connected, like sprinkler attached to the end of a hose but the HOSE not attached to the water faucet.
turn OFF laptop. RESET WRTG54G (there is a small hole you can stick a pencil in there and hold down for 15 long seconds; UNPLUG power.
PLUB back in and hit auto config button.
let WRT54G pick up a new IP ADDRESS from router. once that is done turn on laptop and it should pick up a new signal with new IP address assigned to it by the WRTG54G.