– does the cable have all 8 wires connected? You can do 10 or 100Mb half-duplex with 4, but full-duplex (which gigabit needs) takes all 8.
– link speed hard-set in the configuration somewhere. Let it autodetect.
– switch port hard-set (but less likely on home/small-office stuff).
– drivers not right or knackered somehow. Download latest, uninstall the device in device manager, reboot and give it the new drivers.