Black screen no sound

check every flat cable main boerd to t-con t-con to display if dont help display is a problem

take it to a service center

Buy THIS main board, and replace it. Most of the time, this should fix your no picture, no sound issue.

Those screws are meant for a professional to fine tune the colors. It sounds like you moved the screw too far.

A flashing black screen could have been an issue with the control board. It sounds like it's either time for a new TV or to send it to a TV Repair tech. A new TV might be cheaper.

clean the crt socket if your tv is using a picture tube

does it happen on the any input or just on tv setting?
if it's judt tv then sounds like the tuner, if it's on any input, then the video chip or a decoder on that board.

LCD's use a colorful crystal see through display which only visible when light is shining through it. if you have sound and no picture it's always a faulty PSU. Very easy to change out actually.

Hi,
     If your TV colors get black and white with flickering then there must be a problem of cold soldering(Loosing) and it can be remove from resold, Resold in video section and problem will be solved.
     Thanks. 

I have sound but my tv screen is black. Sometimes when I turn on the tv I get a picture but after 15 minutes or so the screen goes black again.
It's a 4 year old LCD.

Sounds like a convergence problem:
http://www.fixya.com/support/t257424-colors_out_alignment_curved_lines