If other HDMI sources are fine then it's the source. Since the PC is all over the map on video controls it's up to you to find out where to set the resolution and frame rate. It's far from automatic but you will find folk that think it's the TV in such a setup. Hope you figure this out fast.
plugged my laptop with nVidia 360M card into new UN55ES7003 via HDMI and the picture is really shaky. It bounded vertically several pixels and there are artifacts.
If I turn the TV on/off is may clear up for a little bit but returns. I've read lots of comments around the web. Some it could be interlace issues. Maybe set TV to "pc" mode so 1080p signal from laptop doesn't get deinterlaced. DOn't see that kind of setting. Also sounds like an old problem because this TV does 1080p (shows that when plugging in the cable)