This happened to me recently, lol. I carried my laptop downstairs when it was on, and when I got downstairs everything was upside down :)) Took me f-ing ages to sort, and I had to phone my computer nerd brother :-$ If I recall correctly, it's a graphics thing - right click on the desktop and go into graphics options, and it's something to do with rotation - you need to rotate it back 180 degrees. The worst thing is that everything is mirror image with the mouse :))