It will power on but immediately turns right back off repeatedly

I have a 55 inch tcl ruku uhd smart tv and i have tried everything but biying the part that i need cause idk witch part to buy well i can turn it on and it has a picture it says tlc but shuts its self right back off and repeats the cycle i did the restart button ive unpluged it for 20 sec ive held the power button idk what else to do except to find out witch part i need to fix it can anyone help me??