Hi Veronica,
I'm Rodrigo and I will help you.
First, check your network adapter settings, right click the network icon on the taskbar > open network & internet settings > change adapter options > right click your network adapter > Properties > Configure... > Advanced tab > Speed & Duplex (or something similar). It usually is set to auto, you can try to set it to 1Gbps or 100 Mbps to force, but if something else is wrong it won't work.
Try changing the ethernet cable and check if the speed changes.