LAN cable random fail at POST check

So, currently my system is setup to check LAN cable functionality during POST. One day everything is fine, the next there is a failure. I mess with everything I can think of, and it still fails. So, I boot up and open up a browser and there is no problem connecting to the internet...everything seems fine.
The odd part is, when I go into Network Connections, there is no connection listed whatsoever. It's like they randomly disappeared. I try to create a new one, but it tells me to connect to the internet first.....which I already am. What is going on here?

I am running winxp sp2, wired linksys router to onboard nForce network controller. My other computer and game console both have no connectivity issues.