Mac Mini ethernet port does not work at 1 Gigabit

Today I decided to connect my Mac Mini to the router using the ethernet cable and it didn't work. It would connect and then disconnect a minute later. I tried using different cables but that didn't fix the problem. Those cables work when I connect them to my PC so it is not the cable problem. Anyway, after browsing around the support forum, I decided to down grade the connection from 1 Gigabit to 100 Mbps and it starts to work.