Hi @KCooke,
Did you do a hard reset (factory reset)? This manipulation will reset all the settings and put them with the default configuration.
MENU > TOOLBOX > ADVANCED SETTINGS > HORIZON BOX > FACTORY RESET
Then, ennter the PIN (0000, 1111 or 1234).
It will take between 15 and 30 minutes.
Apart the channel guide, do you have other issues such as TV signal interruption? No sound? No image? …
Kind regards,
Michael