How can I extend the display on my PC to use my LG LCD TV as a second monitor?

[Gary 01]

No problem with splitting the image to duplicate the PC monitor.
The problem is when I try to "extend the desktop".
The setting is there in the Windows setup (multiple displays > extend these displays) but when activated the TV screen goes blank (green).
Connected using HDMI out of separate feed from CPU and connected to one of 4 HDMI inputs on the TV.
Any help would be much appreciated.
Thank you.

 

[grebgonebad]

When you say the screen goes green, I dont suppose green is the colour of your wallpaper on your desktop is it? Sorry if I sound patronising. You would be supprised how many people dont realise...