continuous connection interrupted, lag spikes, NEED HELPPP

Ok, so I just got this new computer because my old one just got fried for no reason at all, but that's beside the point. So I hooked up my new computer and my xbox360 is hooked up to my computer, which has a wireless (******) connection to my router in the basement. So it's like a combined wired and wireless connection. This has been my setup for over a year now, and worked absolutely perfectly until I got this new computer. It doesn't make any sense to me why now I would have these connection problems. I can get on live, connect to everyone hear everyone and all that. It's just I can have 4 green bars in CoD and yet get connection interrupted about 10 times in a single match. These lag spikes last for like a second, but then they end for another minute or so. Along with that I just get miny lag spikes for about a second, but it still ruins the gameplay. I've looked around and I can not figure out why in the world this is happening. I can no longer play competitively online until I can get this fixed, so does anyone know WHAT'S WRONG?!?!?!

no, Ive had this setup for a year and never had any sort of problems. and also idk how to check my nat on xbox anymore with the new dashboard, it doesnt just show it when u test your connection like it used to. the card is live compatable, i changed computers i still have the same wireless thingyy.