Solved - It was a combination of checking the box which allowed the window manager to control the windows and then holding down alt to scroll down to the dpi slider. Many thanks for your prompt expert advice everyone. I am most grateful. Anyone have the slightest inclination why the mouse disappears when I try to play the game? When I move the mouse into the running game it disappears, but is still usable - eg, when I click it responds accordingly, I just can't see where I've clicked.
