That's usually a control board failure, and these can happen suddenly.

If the system shows the same fault through a screen test -- hold D through powerup to access -- it does need to be replaced.

I press the power button and all I can see is this white vertical lines. Can you please elaborate a little more how to repair this? 

The technician applied another screen to check the screen. The other screen worked fine when he powered the laptop.

Does that mean the screen is faulty or is it still the control board?

The control board is part of the screen - it's not separately replaceable.  You need a new screen assembly.