Can't connect at 1000mbps, only 100mbps

Problem: Had a computer with a nice, new on-board Intel NIC. It would only connect at 100mbps. I even put another Intel network card in that was working at 1000mbps on another computer and it still wouldn't work. The internet was also running very slow.

Solution: I forgot that I had setup the network in that office to run the network cable through the network power filter on the UPS. Set it up the normal way and everything was back to normal.