A few weeks ago my cat walked across my laptop keyboard. Suddenly the picture on the screen was upside down. Try using the mouse when up is down and down is up - if you see what I mean!! Short of standing on my head something had to be done. I had to work out how to rotate the picture on my screen.
There are 2 solutions to this.
1) hold down the ctrol + alt keys. While holding them down press one of the 4 arrow keys.
Up arrow = picture right way up
Down arrow = picture upside down
Left arrow = picture facing lhs of screen
Rigth arrow = picture facing rhs of screen
2) Right click on the desktop, select graphics options and then rotate (I'm using Windows Vista)