Hello.
First, check that the network cable is securely plugged in at both ends, ensuring it isn't loose or damaged. Then, try unplugging and reconnecting the cable at both ends, or replacing it if necessary.
Is the computer's network cable connected to a wall LAN socket or directly to the router's Ethernet port? Are the router and computer in the same room, or are they in different rooms or on different floors of the house?
Please specify the exact computer model or motherboard model, or go to Start, type "msinfo" in the search box, and attach a screenshot of the System Information page.
Right-click the Start button > Device Manager, expand "Network adapters," and post a screenshot.