When there are no signs of activity at the Ethernet port, the PRIMARY and SIMPLEST troubleshooting step is to check the physical connections. Inactive port LEDs typically indicate a physical problem, such as a disconnected or faulty cable or an improperly seated connection, which is what you can quickly and visibly inspect. Should this fail to resolve the issue, one might then consider potential hardware failures, settings misconfigurations, or distance from the wireless signal source if applicable, but further steps would not address the immediate problem displayed by the unlit activity LEDs.