Try plugging DVI from monitor to PC, and use HDMI to monitor. Don't turn them on at same time as the monitor can't accept two signels. Why the switch, too maany connections? Are you sure the LG is a monitor, I got nothing on their website.
Just if anybody wants to know how i solved it for my setup.
It was a problem in my catalyst driver settings. Since the UI is terible, took a while for me to figure it out. But, if you go to
desktop and display ---> right click the small monitor button on the left --> configure --> pixel format tab ---> i forgot what mine was set to, but i chose 4:4:4 RGB FULL and the picture quality is similar.