On Top of the remote next to the power button is a TV button. Press the TV button and then the power button. You may have to powered up first and you should find these controls on the side of the TV itself. If this does not work you may need a new remote. Good luck
Your batteries may have been good.
You can put your cell phone camera in front of the remote IR LED to see if it is blinking. It is invisible to the naked eye, but can be seen with a digital camera.