The game is quite mathmatical so: If you get the entrie grid 
full of noughts, instead of crosses, then simply press each 
tile in order in a clockwise spiral inwards. This will turn 
them into crosses. With a group of four tiles (2x2), pressing 
each one in turn will reverse them completely and have no effect 
on the other tiles around them. eg. OO XX OO becomes XX OX XO XO 
becomes OX XX OO OO becomes XX etc...