NIC would be my guess.
Is your NIC wireless or wired. They can fail in a way (if hard wired) that the NIC can mess the router up. I don't know what happens, only that I have seen this.
Otherwise I agree that it is probably the router.
Wireless. And i used to have issues connected to my roommates router at my old place (due to the NIC), but they vanished when I moved. I used to use my laptop as a bridge but even that has failed for this problem.
Of course since I posted this I haven't had any issues. Rubber duck method really works well I guess.
