I have a very old TV, model 24PW6301/02, and as I turned on the TV this morning, my remote control didn't work properly:

All buttons don't work as they should be. Their functions are now suddenly under different buttons, e.g. the on/off button is now mute, going a channel back is now "3" and "1" is now channel "9".

What happened here, but more importantly: how can I get it back to its normal state? Can anyone help here?