The screen was black

Kyaw Aye Hlaing 
in a darkened room turn the TV on to a channel where you have sound etc. Then us a flashlight and shine it at an angle against the screen see if you can make out shapes silhouettes etc. If so you know that your backlight is not working. This may require replacing the LCD strips inside the panel or a new power board. You will have to remove the back from your TV and check the power board with a multimeter Post some good images of all of your boards with your question so we an see what you see. Adding images to an existing question

If you cannot see anything (triple check) then it is possible that this is a bad main board or a bad t-con board as wella s the panel (unlikely but possible)

Of course before all of this. Unplug your TV, unplug all devices that are plugged into your TV and then hold the power button down for about a minute or so. Then plug one video source (preferably a local DVD/BR or Game console)in and plug the TV in, restart. See if that resolved it since a bad cable box can sometimes cause a dark screen as well.
TCL does have issues with subpar backlight LED strips.

Hi,

When you can hear sound and no image, this is almost always the backlight pannels that are burnt.

Try using a flashlight to see if you can noticed to image in the TV. It will be very very dimmed since there is no more backlight.

If so they would need to be replaced. In some rare cases it may be the power supply board supplying power to the lights, but the vast majority of the time, it’s the lights themselves.

Very common failure in led TV

I hope this helps