You will need to leave default router blank as you are not using one. As for the IP address, you will likely need to leave this as Automatic so that the system will use the one assigned by the internet provider.
The DNS addresses you likely found were correct. i would suggest unplugging the power from the modem for a minute then plug it back in again. When switching the modem between machines you need to turn off its power to free up the IP address given at the time..