TylerG,
I apologize in advance if this suggestion insults your intelligence, but we all sometimes do things in a hurry and make silly oversights.
It's what you said about only one person being able to connect -- which, I assume, included you and your brother, both wired... That is precisely what should happen if you had a cable modem plugged into the LAN switch side of the router. The first computer would probably succeed acquiring an address from the cable modem directly, but any others would fail.
Make sure that you haven't done this. The modem needs to go in the port marked "WAN", "Internet" or something similar.
