Screen is dark when I flip it open

What is your phone model?

These answers were given assuming that you're using a LG smartphone with a touch screen :

Scenario 1 : Can you see the screen lights up and any sort of graphical image when you hear incoming message ?
A : If you can, and still you cannot slide unlock, your touch screen has gone. Get a replacement touch.

Scenario 2 : You cannot see anything on the screen. It stays dark when you hear incoming messages/calls
A : Your LCD has gone. A replacement LCD or a Touch/LCD combo would fix the issue.

I hope you saved your back by either way.

The problem is not the video board but the light behind the display that makes it viewable. Some tv's use LED's, others use tubes, but taht is the problem. You cant fix it unless you can get the inverter board, but if its LED you dont have an inverter board. It is another board I cant think of right now. Go to ShopJimmys TV and they can help you. He is an expert on this stuff. I called them after looking at their videos on youtube. it can be fixed depending on set it might be worth it or not.

If you have done this kind of repair before, you could look on eBay for a replacement screen and price will vary. If you don't know how to perform a repair of this magnitude, you;re better off and will come out cheaper just buying another phone. If living without text doesn't bother you, no loss.

What happened in the first place to make your lcd screen go out? there is a chance that the problem was not the screen, but the phone it self. did you drop it in water, or jus cracked screen?

if you could see any image from the broken lcd before changing it so your new lcd is not working or no installed right
and if not you may try the cable or the hard shock that broke your lcd effected the main board

That most probably means that the display connector between the flips is torn.
It happens with flips and slider phones.
Contact to the nearby LG care center.

open messasge-click options-extract data-highlight the address

replaced the LCDS on the phone

Is it a flip flop type of phone or a slide type.?
You need to eplace the flex wire of that phone 'coz that's the
usual problem of all flip and slide type of phones

Just replace the LCD.