It's plugged in to the same hub as my main machine and I can't even access my router UI.
Is this an actual hub or do you mean router? If it's a true hub and it's then connected to the modem, your modem will only hand out ONE IP address.
Try this, unplug your other computer and only have the new computer plugged in. Unplug the power from the modem, wait 5 seconds then plug the power back in. When the router has completed booting, turn on your laptop. You can also do this without the hub and just connect the laptop directly to the modem. Just note that when ever you change the network you need to power reset the modem.