Reinstall OS? That's the only way I was able to get it back.
I have a Linksys LNE100TX 4.1 NIC, and if the LAN worked but the internet went out, it did some funny stuff. Eventually it got to where I couldn't go into network properties, nor do an ipconfig /release or /renew.
I don't know what did it, but a new install fixed it. Maybe try installing/uninstalling service packs?