Black Horizontal lines on screen

[orororor]

Black Horizontal lines are appearing on the bottom part of my screen, first it was a thin black line, now there's two of them.

 

[kep55]

I have that problem on our LG 50LN5400 tv. Plus, the lines "jitter".

 

[kep55]

The gang @ Tom's have no idea what's causing this. IT'S THE END OF CIVILIZATION!