Hello, I'm TV Tech1 and I'll be working with you to identify and help you resolve your problem.
Do a couple voltage checks and listen for any relay clicks first.
You see the main board that has all the video input connections on it? That board tells the power supply board to actually turn on it's DC voltages going to the rest of the boards. Since you don't see the red standby light anymore, I suspect the main board isn't getting the Standby 5 Volts needed to turn on the main board so it can control the rest of the power supply board.
Look at this picture, it's a picture of your TV set's power supply board located in the Top center of the TV chassis. Your power cord connects to it, and that's where you want to concentrate your tests on. The picture has information written into it, and you really want to see if you have Standby 5 Volts FIRST, the relays do or don't click 2nd, and at least try to find the PSON pin, measure it, see if it switches between 5 and 0 Volts when you press the TV's power button. When you do the testing, put the black test probe on the metal frame since that's ground, use your red probe to test all points, and make sure your DC voltmeter is set to DC volts.
There's a main cable that connects the power board to the main board. On it you should find a pin that's labled STBY 5 or STBY 3.3, depending on the type of microprocessor it uses. You should find that marked on the Power supply or main board end of that plug.