There could be some process eating up your bandwidth. You could have a look in Control Panel\All Control Panel Items\Administrative Tools\Resource Monitor about the processes network usage. Have you tried downloading a large file to check the speed you'll be getting. Sometimes speedtest.net isn't a 100% accurate. I've seen it show speeds of 80Mbps for people actually getting about 24Mbps or showing way less than the actual speed because of some weird Flash Player/Browser misbehaviour. Do you have the same problem when using ethernet connection/wireless? Have noticed if the speed is slow since you boot the machine or if it's slowing down gradually?