Ensure your remote's batteries are not depleted. Replace if necessary.
Press the 'Menu' and 'Home' buttons simultaneously for 10 seconds.
Disconnect your TV from the power source, wait a minute, then plug it back in.
Hold the 'Home' button for 10 seconds to pair your remote with the TV again.
Ensure your TV's software is up to date. Go to 'Settings' > 'Device & Software' > 'Check for System Update'.
If all else fails, perform a factory reset on your TV. Remember, this will erase all your settings.