Apple TV remote only makes the light blink.

It was working fine a few days ago and there haven't been any updates as far as I'm aware so what the fudge! When I attempt to use the remote, it will make the light on the box blink 3 times and nothing else. I'm not able to navigate at all. It's a battery operated model so I've replace the battery. No change. I've unplugged the box for far more than 6 minutes and plugged back in again. No change.

I've pressed and held the menu and every other button in a sequence. They all seem to "reset" the box (light flashes until I release hold of the buttons). No change. I'm not able to unpair the remote and TV as following the instructions just leads to more lights blinking and no broken chain symbols.

I'm at a loss. Any suggestions/advice will be most warmly welcomed.