Go to the top of the list in device manager and right click on your computer name then click on scan for hardware changes. If this does not do anything go get the driver for your network card and run that it should add it back.
click start type devmgmt.msc that will open device manager. In the picture below you will notice an icon of a pc with a magnifying glass over it (toward the middle, along the top of the box)
click that and it will search for hardware that is not installed.
If it doesn't show in hardware manager(either with or without drivers), then Windows doesn't see it and drivers won't help. Can you see the NIC in Bios? Is it disabled in Bios or Device Manager?