Thank you very much, Lise, for your response. But that hasn't helped so far.
I've already been upstairs and seen the clue. Clicking inside the clue causes some of the numbers and symbols to disappear. I'm left with three numbers - 0,7,1 and a triangle. All possible combinations didn't work.
Also, clicking the "?" clue button when in close up of all the numbers gives a pictorial clue, with all numbers shown, but 0,3,6,9 as the prominent numbers. Still no luck with combinations of those numbers.
Perhaps another gentle nudge?