Try setting the display mode while in safe mode. When I see this I try lower settings such as noted in the manual at http://www.lg.com/us/support-product/lg-55LF6000 I see these listed at page 19 of the English manual. Try 800x600 at 60 Hz and work your way up.
I am unable to get my HTPC to appear on my LG via HDMI.
The TV displays all of the boot menus but cuts out right before getting to the desktop. Oddly enough I can get the input to display fully while I'm in Safe Mode. I've tried unplugging everything and plugging back in but no dice. Are there any other suggestions to fixing this?