Hi Gaby.
First, check that the network cable is securely plugged in on both ends. Then try unplugging and replugging it, or replace it if necessary.
Is the computer's network cable plugged into the LAN wall socket or directly into 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 model of your computer or your motherboard, 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.