My LG TV has a flickering green, purple and black lines LG55LW5500

TV display is not working at all. This is an LG LED LCD model number 55LW5500-CA manufactured in Feb 2012 and we bought this in Hong Kong in 2012.

There are horizontal flickering purple lines in the lower 75% of the screen and green/black lines at the top (see image attached).

These lines keep flickering and nothing is ever visible. However, the audio is working and i can hear the sound of the programme / channel that is on. I can increase the volume too however the visuals do not appear at any point.

This happened while the TV was off - it didn’t suddenly go from working fine to the flickering lines.

Please can someone suggest (a) what might have gone wrong (b) whether i can replace / repair that part myself and (b) if this is beyond repair, where can i get help?

Thank you very much.