OK, there are two possibilities for this kind of problem, either power supply board isn't providing volts to main board due to internal failure OR main processor chip isn't working mounted on main board which controls all TV functions including power On-Off, this could be either failure of main processor chip or EEPROM (memory) chip that stores TV firmware data thus main processor chip doesn't boot up.
You can check output volts of power supply board with multimeter to see if it provides standby 5V DC output that is necessary for main processor chip to wake up, if standby volts isn't available then replace power board in TV which will help to resolve the problem.
if standby volts are present then main board of TV will be replaced to get the TV up and running, please check with following board supplier with your TV model number to get required replacement board..
If you are not comfortable working on it yourself then you may please use following link to get list of TV repair shops in area which will help to get repair quote...
I trust my input will help you out. Please feel free to respond if you have any additional questions.
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