It suggests to me the Network adapter is either disabled, in the BIOS, or it has failed.
To check it is enabled, enter the BIOS / Setup as PC starts and look for the LAN adapter, usually under Integrated peripherals, or similar.
If Network adapter is enabled in BIOS and it is still not found it suggests the device has failed. A replacement card is cheap and easy to install. An alternative is to buy a USB wireless adapter £7.50 from PC World.