What can we do if a network interface cards (NIC) is not working?

Issue

What can we do if a network interface cards (NIC) is not working?

Solution

Sometimes network interface cards (NIC) of new hardware do not respond when plugged with network cables. Below are suggested diagnostics can be done before replacing the hardware,

1. Try different network cable.
2. Is the NIC's LED blinking if network cable is plugged in? If it is, then, What is color of the LED? Solid amber color shows malfunctioning of the card, NIC needs to be replaced.
3. Try a system power reboot. Shutdown the server gracefully, unplug power cables and wait for 3 minutes, then re-plug power cables and restart the server. 
4. Try re-seating network interface cards. Un-plug and re-plug NICs may fix the issue.

The above basic diagnostic operations help to understand the status of the hardware. If these steps do not solve the issue, then a replacement is suggested.