Rename the HDMI input that you are using to "PC"
PC's and TV's process an image slightly differently, and if you don't manually set the HDMI input to "PC", the TV assumes its a TV type input, which results in a VERY blurry image.
I ran into the same exact problem with my Samsung UN40C7000 a while back.
Have been plagued by this problem for months. This solution fixed it - thanks very much. Who would ever have guessed renaming an input would make any difference?