The most likely cause of the issue is that the port on the switch is faulty since the cables have been tested and found operational, and the server is newly deployed. A bad port would prevent the LED indicator from lighting up and would lead to connectivity issues. If the cable were disconnected, the LED would also be off, but this scenario was ruled out since cables were confirmed operational. A wrong VLAN assignment would not typically cause the LED indicator to be off; it would rather allow the server to connect but potentially to the wrong network segment. A duplex mismatch would still usually allow for some connectivity, albeit with potential performance degradation, and the LED indicator would not be completely off.