Another thing you can do is follow your cable line to the box. If you have any splitters on it remove it and directly connect it from your modem to your computer. Also, you can call your cable company and see if they have any signal amplifiers they can install for you.
My house for example is getting 15 Mbps from my internet company, I was only receiving 5 - 10 Mbps which is decent, but not what I was paying for. I called them and they found several splitters attached to my internet line which raised my speed to around a steady 10 Mbps, still 5 Mbps short. Then he installed a signal amplifier which boosted the weak signal I was receiving back to 15 Mbps the moment it enters the box. So, since it has such a short distance to travel I get around 14 - 15 Mbps download speed now.
Once you do that, if I were you, I would delete my operating system partition and do a fresh install of Windows 8 on a new partition. Only do this if you know how because you could mess up your computer if you do something wrong.