Thanks for you replies.

When I want to turn on the TV, I select it first and the push power and it turns on. When I hit power again it turns off.

If I push TUNER instead, and then Power on, it won't turn on. But if I turn it on by pushing the button manually, then hit power on the remote (having previously selected the tuner), it will turn off.

It was working fine before I fumbled the remote while doing the volume punch through. Is there a way to do a "factory reset" on the remote?