LG 47LM9600 Owner's Manual page 200

PC connection problem
Problem
The screen display is not
on after connecting to
the computer.
There is no sound after
connecting the computer
with the HDMI cable.
Verify that the computer and the TV are securely
connected.
Turn the TV off and back on using the remote control.
Restart the PC with the TV on.
Check if the resolution is correctly set for PC input.
To use the TV as a secondary monitor, check if the
connected desktop or laptop supports dual monitor
displays.
Check with the video card manufacturer to ensure it
supports HDMI voice output. (Video cards manufactured in
DVI format require connection of a separate sound cable.)
Solution