I have a total black screen on my tcl 55” model 55s405I

I have replaced the main board and the t-con board but still no picture. Powers on and I can click and hear sound.

no back light when I do the flashlight test. Once in a while when I power on I get a quick glimpse of tcl image but then goes black… I purchased 9/2019 and because i can’t produce receipt tcl won’t honor warranty.