No Default Gateway with Vista, no internet

Hello,
Have an HPm8200n, one day my integrated LAN stopped working, bought a linksys ethernet card and connected alright, but was really slow. Found that the card did not support vista (but could still connect, like I said, just slow). Switched to a Netgear PCI card, could not connect at all. Put the Linksys card back in, still couldn't connect.

Determined that when I go to ipconfig, I have a default gateway that is blank. I've been pulling my hair out trying to figure it out. I've done the hardware check, the network diagnosis, etc. etc. Talked to some IT guys at the office (I'm obviously not too harware literate), said it sounded like the motherboard was bad (considering the onboard LAN had gone out first). But the PCI expansion slots work, just not with an ethernet card. It says in device manager the card is working properly, drivers are up to date, etc.

So I changed out the motherboard (first time, kind of interesting, not too difficult, but I took more time than I probably needed). Changed CPU and everything. Loaded the drivers for the new motherboard, everything is working fine, except of course I have the same problem......no default gateway in ipconfig and no internet connection.

I've reloaded windows, did a recovery of the origingal system specs, etc.

Any help would be appreciated. Thanks