If the TV screen keeps black and no audio but the backlight is on, please power cycle the TV.
You could unplug the power cord from the socket and plug it back in.
If the issue cannot be resolved, please feel free to call the TCL hotline for further help.
Note: To check the backlight, you could use your finger to click the panel of the TV slightly.
If you could see the flashing white light, it means the backlight is on. Here is a picture for your reference: