The computer was built in 2010 and has been operating just fine since then. The ethernet port had been questionable before as it would require a re-plug into the machine or switch maybe once or twice a year for some sort of "jumpstart" effect.
The computer was left in Windows 7 "sleep" mode for a duration of approximately 12 hours since it last functioned correctly and was set to sleep. No abnormal user operations before issue. No network connectivity modification prior to issue. No power source conflicts. No changes to the network. No other devices on same local network reporting failure. No driver errors reported by Device Manager. No changes to issue when using different ports on the LAN switch box. Different CAT cable did not help. Reboot did not help. Safe mode with networking did not help. And weirdest of all, it works absolutely fine with a Linux Live CD's NIC driver set (no errors detecting hardware or network or connecting to network).
The card is a 'Realtek RTL8168C(P)/8111C(P) Family PCI-E Gigabit Ethernet NIC (NDIS 6.20)' and is an embedded NIC on a GIGABYTE G41M-ES2L motherboard. Device Manager: "This device is working properly". Using a Microsoft provided and signed driver version 7.2.1127.2008 dated 2/26/2008. As I said, it's been working fine all this time.
Briefly: Windows 7 no longer can detect ethernet network, but has working hardware and drivers and two years of functioning history. Ideas~ go!