Internet problem

[KaraK [T]]

Since yesterday morning, I've been having trouble with my internet connection.

Most websites are loaded normally, though sometimes it won't load it properly until I refresh the page.
Streams on Twitch.tv are laggy, in the way of pausing the stream, then playing the missed time sped up and getting back to live. This happens (it seems) randomly, but on every stream.
Microsoft Security Essentials couldn't update due to 'a problem with the internet connection'.
League of Legends will let me log in, but after maybe 1 or 2 minutes, I lose connection to their servers after which I can no longer chat or queue.

I am connected to my router through a cable. The router has wireless, but nobody is 'stealing' my internet.
Restarting my router and PC internet connection didn't solve the problem.
Speedtest.net result on the bottom of this post.
Network usage in task manager shows 0-1%.
The Housecall virus scan showed no threats.

Anyone who can help me out here?