I'm trying to decide very close problem: from time to time network card stop working. Symptoms: sign in lower right corner show, that I have no access to network and network card don't react (mostly) on disabling/enabling. When I reboot computer, network card start as disabled in Windows (not in bios). I'm tested that situation with Windows 7 x32/x64 and with Windows XP everything is OK. So it seems to me it's a driver problem.
I switched off "Wait for link" in Advanced tab. Hor last 10 hours system works fine. You may try the same. Let's see result.