With all, or most LCD tv`s ones that are about three to five years old.
It always comes down to the main power board of the lcd tv.
For any faults to do with no picture on the screen at all, or coloured banding lines present on the screen either vertical or horizontal in orientation on the display screen.
Some may exhibit powering on problems, or take much longer before any sign or image of a picture even corrupted colour bands being produced.
Or will when powered on, you will see a quick flick of light where the back white light set behind the main lcd screen it`s self attempt to power up.
This is so you can see the image actually produced by the lcd matrix of the screen.
In most cases, all it involves is opening the Tv if out of service warranty.
And looking at the main power board.
Due to heat the first components likely to fail are the capacitors of the main power board, the ones mainly or most critically damaged will be the ones closest to the hot areas on the power board.
Places such as where the transformers of the main power board sit.
And where mosfets or voltage regulators reside, where they are attached to a large heat sink plate.
Visually look at each capacitor, any that show they are domed at the top of the capacitor are the cause of why the Lcd tv does not power up right, displays no picture, or produces random vertical or horizontal coloured lines of the lcd screen.
Simply read off the voltage of the capacitor and it`s farad rating.
replace all of the caps that are domed with a like for like capacitor in voltage and farad rating Ie: 35v @ 1000uF
Making sure you place the new capacitor in the same orientation as the old one where the stripe is indicated.
If you can solder to a degree this is easy and will cost you no more than a few £ or $ to fix the set.
If you are reluctant to do this.
Simply locate the model number of the power board and all of the serial information on it and you can find a replacement power board for it along with the model number of the Lcd found on the back of the unit and it`s brand name.
PS: You would be amazed at the amount of LCD tv sets thrown out all because of one or two faulty capacitors costing no more than 25 to 30 pence to replace them.
I see it all of the time and picked up a 60" Lcd tv up from a local tip for nothing, replaced one single capacitor, and it was in perfect working order after it.
Wee live in a society where it`s easier to throw something away and simply replace it in most cases without question because we think it will cost more to fix it without much question sad really.
In your case I`m glad you asked how to fix it Muath.
And if you open up the Tv you will no likely see exactly what I have explained to you as to why the tv is not currently working right.
But if you follow the advice here and replace the caps it will all work fine.
The link is to a picture of what I have been talking about, as a visual example of a bad capacitor, any liquid or fluid escape is also deemed as a bad capacitor even if no doming is present.
Other tests visually use a straight edge place it on the top to see how much the capacitor is domed.