Marvell/Aquantia AQC113CS (10Gbps) Firmware Version 1.5.42

Try: shut down & power off the system. Then unplug the ethernet cable & the PC's power cord. Then press and hold the front panel power on switch for several seconds, to discharge the PSU capacitor.
Then re-plug the power cord & power the system back on, to see if the LAN port has re-appeared in Device Manager.