What motherboard is it on?
Try again with installing the driver
What OS are you using?
O/S and motherboard were known issues, but really looking for the vista driver for Realtek RTL8169/8110 family Gigabit Ethernet NIC.
The link I gave you has all OS drivers, get this one "Vista
and Server 2008 Auto Installation Program (SID:1655713)". It's the first one on the list.