Also:
http://compnetworking.about.com/od/windowsnetworking/f/cableunplugged.htm * Disable the Ethernet network adapter if you are not using it. This applies, for example, when running a WiFi home network with computers that have built-in Ethernet adapters. To disable the adapter, double-click the small Network Cable Unplugged error window and choose the Disable option.
* Check both ends of the Ethernet cable connected to the adapter to ensure they are not loose.
* Replace the Ethernet cable with a different one to verify the cable is not damaged.
* Update the network adapter driver software from the manufacturer's Web site.
* Change the Link Speed and Duplex settings (using Device Manager) to use "100 Mbps Full Duplex" or "10 Mbps Full Duplex" instead of Auto Detect.
* Replace the Ethernet network adapter if it is a removable PCI or PCMCIA card.
First remove and re-insert the existing adapter hardware to verify the card is connected properly. If necessary, also replace it with a different card.
* The device your Ethernet adapter is connected to, such as a broadband modem or network router may be malfunctioning. Troubleshoot these devices as needed.