To troubleshoot HP laptop Ethernet cable issues, begin by inspecting the cable for any visible damage. Ensure it's securely plugged into both the laptop and the router or modem. Try using a different Ethernet cable to rule out a faulty one. Restart your laptop and networking equipment. Check if the Ethernet port on the laptop is functioning by testing with another device. Update the Ethernet driver in the Device Manager. Disable and re-enable the Ethernet adapter.