LG DU-42PX12X Verticle lines of various colors, and widths throughout the screen.

It will be best for you to visit the site linked here. It has screen-shots to defective LCD screens, and details about the faults. You can compare them to that of your TVs' and can determine the cause of the fault. If you wish to get more details, check this. http://electronicshelponline.blogspot.com/
Pull up previous posts by its left sidebar, or type in the brand name and model number to of your set, to its search box, and press 'Enter' or view it in Mosaic / Timeslide option.

Bad Tcon board or the cable going from the board to the panel, try that first by cleaning both ends if that doesn't help you need a new board

You didn't say weather the lines are verticle or horizontal, but if the lines are verticle check the circuit for a weak capacitor or if the lines are check the horizontal circuit for a weak capacitor. During your check check for cold solder joints, idf you come across ant re-solder then. Good luck.

MINE DID THE SAME THING ABOUT AN HOUR AGO. I UNPLUGGED THE SKY BOX FOR ABOUT 10 MINS PLUGGED IT IN AGAIN IT WAS FINE

My LG RT-42PX11 after a few minutes the screen starts to flicker and colors go psychedelic and after some time no picture at all

You need to describe these lines better. Are they moving or stationary? Are they very fine lines with sharp edges or are they more like bands with soft edges? How many lines do you see, and how wide are they (compared to the screen width)?

Fine lines that are stationary: defect in the electronics causing a vertical row of pixels to be dead or stuck. Can only be fixed by replacing major parts.

Broad lines with soft edges that move: could be electrical "hum" interference. Make sure you are using a grounded (3-pin) power plug, and that the outlet is properly wired. (Take the TV to a another location and see if the problem goes away).

Make sure you don't have fluorescent light fixtures nearby--they can interfere with the picture if the bulbs or ballast is defective. Could mean tecon board or display is bad which means replacing both in a sony if they are bad i recomend buying a new tv because it is not cost effective to replace these.

As i understood the explanation you have a problem with the Video card not the LG Monitor.

Replace the timer control board

This is a common problem with LCD screens. It is pixel line damage and the screen is permanently damaged and is not repairable. It will probably get worse. The only answer is to replace it

I had the same problem on my DU-42px12xc. Red, green , and blue lines vertically on the right side of the screen. I found a loose solder connection under the inputs board on a resistor. After re-soldering, everything was crystal. I'm happy I grabbed this tv before my work threw it out. Be very careful when soldering SMT components. Use proper equipment. I had to troubleshoot while the tv was on, so I was extremely careful not to short anything out.

I pulled the inputs board out to gain access to the "Y-axis" pins.
resistor located under the inputs
I started pushing on the resistors 'till the color lines started working correctly, and re-soldered the four resistors.