Wireless issues for all computers except one?! HELP!?

Before I get started, I would like to note that I am relatively noob-ish with this kind of thing. PLEASE EXPLAIN WELL. Now...

I have a Netgear Work and Play N300 router.

(http://www.netgear.com/home/products/wirelessroute...

For a while, I've had no issues at all with this thing. Then I decided I wanted to do some living room re-arranging. In order to do so, I was going to have to unplug my Cisco cable modem and router. As soon as I got everything hooked up again, both my fiance's and my Macbook Pro can't seem to connect to the router. We get this self-assigned IP error. So then I just tried using a manual DHCP address in the event there's an IP conflict. It would work, but internet would be extremely slow and eventually drop out. I have Windows 7 on my Macbook and tried that, and it strobes between "Limited Connectivity" and "Internet Access" status. My main computer is the only one that works flawlessly. Even when it's turned off, my laptops still have this issue. I've tried everything under the sun and then some. I really don't want to keep factory-defaulting my router, because this isn't the first time I had this issue. Please, it is imperative my fiance and I have working internet on our routers. We're college students and we can't keep sharing the one working computer all of the time.

Things I remember trying

(obviously) resetting router/modem.

Calling tech support monkeys (they never really help).

Calling ISP (nothing they can do on their end)

Factory resets

Replacing modem

No matter what I try, I end up with the same eventual issue.