Motherboard:  GA-Z68X-UD3P-B3
Revision:  1.0
BIOS:  F5
CPU:  Intel i5-2500k
Memory:  Gskill F3-12800CL7D-4GBECO DDR3 1600 (PC3 12800)
OS:  Windows 7 and Ubuntu 11.04
Purchased my first Gigabyte motherboard, and all was fine for 10 days.  Then the onboard network interface stopped working.  Windows could see the device, but believed a network cable was not plugged in.  Tested multiple cables on a different system, and the cables worked fine.  There is no link/activity light.  Tried loading optimized defaults in bios.
Returned the board for a replacement, and the replacement is doing the same thing.
I feel like I am missing something obvious, but I'm not sure what else to try.  Any suggestions welcome.
Thank you,
Karl