Triggers/Conditions - Hollywood Squares Game

I am trying to build a game playing against the computer (tic-tac-toe).  The player picks a square, which triggers to layer asking a question.  The player answers correctly and returns to the game board.  I added triggers to change the state to show X (visited) and gray-out the figure, which indicates this square was already chosen.  

Button status: Normal (not played), Visited (played by X) or Disabled (played by O)

The game board also has a button for the computer's turn (O).  The player selects this button and I built the trigger to select one of the squares for O.   The trigger changes the button state to disabled under the condition the button state was normal.  I believe I will need a second step here too.  Where to tell he program to go next if the button state was visited.  (tricky part because you don't know where the player will go next)

I believe I am on the right path, but can't pass the finish line.  Any help would be appreciated.  I added notes to the course to help guide you.   :)  Thank you!