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Sounds like the input source to the TV has been inadvertantly changed, but why usng the TV remote would afffect this I do not know.
Don’t have a Sony TV so this is guesswork until some one eho does perhaps posts better info.
If the Humax remote has been set up to control the TV try (with the Humax on)
Press TV on Humax remote:
Press source button (bottom left hand side button) this may either – cycle the input sources so eventually the picture from Humax will appear, or bring up a menu on screen for you to select the input, if that is the case try each one in turn.