While this is almost never it, please be sure to go to:
Right click on My Computer, choose Properties, select Hardware, click on Device Manager, right click on your NIC, choose Properties, select the Power Mangement tab and make sure the "Allow the computer to turn off this device to save power."
That should NEVER be checked.
I have no idea what Windows was thinking. Having that feature on, must save about one-cent per year.
