there is no usb or sd card in the tv. the tv is BUSH model number A637F
sorry i forgot to say yes the tv power lamp does respond each time i press a button.
Ok, we DO KNOW that the TV is supplying your STANDBY POWER to your TV's MICRO. The lamp responds. Now that MICRO sends a signal back to that power board, and it's supposed to turn on "The rest of the power supply" Actually turns on a 12 volt section and also a higher voltage section that makes the LCD panel glow a subtle gray light level about a second after you press the power button.
I don't know if you happen to have a voltmeter, and if you do, it can tell us is the power supply is being turned on by the main board or not. Since power supplies develop DC voltages the TV can use, we can look at the markings on the power supply and measure certain pins on one of the plugs on the board to see if the main board is turning on the rest of the power supply, and if the power supply is creating the needed voltages.
I have a picture of your power supply board, but the focus is too blurry for me to read the markings on that plug. I need your eyes, OR your digital camera to go on to the next part of the test. If you do have a voltmeter, I'll show you how to test it, and if not, I'll have you double check a couple things that may point us in the right direction.
Look at this picture, respond back about the voltmeter and also if you do or don't have a digital camera. Considering the fact that those cameras have been around for 20 years, I assume most of us do have one.