Lan connection trouble can't figure out the problem experts i need you

I have lost my internet connection on my computer. It is wired into my 2wire router. All the lights on the router are working, in fact I have a laptop which is wirelessly hooked up to this router which works fine. Also, I have a second computer wired into the router that is getting a connection as well. So, I believe we can assume it is something on the main computer that is causing the problem. It has very strange symptoms. It will work for a few minutes and then simply just stop working. I have noticed if you try to do any downloading of video or anything larger it shuts off much more consistently. When it does stop working it shows on the details page that packages are being sent but none are received. In fact when it goes down I can not even get to the router from the local ip. It's like i'm losing the connection somewhere in my computer before it gets to the router. I have looked at my tcp/ip settings and dns and ip are configured automatically. I have removed every possible firewall i could find and looked at every setting possible. In fact how this started was I got a new video card and unistalled the drivers for it. What I did not realize was the motherboard had nvidia drivers as well so i lost my pci bridge,sm bus,ethernet. I re-installed a fresh copy of windows xp pro, added the motherboard drivers and noticed that the lan connection 2 which was the onboard ethernet would say lan netrwork unplugged. After trying everything i could I figured i would try to bypass that onboard network controller and purchased a pci ethernet card plugged it into motherboard.So, then i had lan 2 (nvidia nforce network controller) and the new card on lan 3.At this point was when I was getting the internet connections that went off and on. Most of the time when it does go down if i disable then enable lan connection 3 it will work for a small bit of time. Sometimes it gives me the cannot renew ip error. Any ideas what is wrong or what I can try next to fix this computer?