I just build a new desktop PC on the weekend and want to use wired ethernet to get online. We have the latest BT home hub (UK) installed - as well as all current drivers for the mobo/lan connection.
As soon as I made a connection with this new PC via a wired connection, our entire network is running incredibly slow. For instance, it's taken about 25 mins to download a 30mb install for Steam. Before this it was totally normal.
All other wireless devices have had the same speed issue since I made this new connection. What could be causing this? For reference, we have about 3 wireless devices in use at any time and 2 wired PCs (including my new one). I'm also on Windows 8.1...
Be sure you don't have any internet hogging services on the windows 8.1 pc, such as any p2p like utorrent. Also with all the crazy stuff people are putting out there these day's I'd run a good 3-4 passes with any virus/malware scanner.