"I acidently did by acident today"  *snickers*
     
OK ok, this should be an easy enough fix...  Do you have an nVidia crd?  If so, rightclick on the desktop, click proporties.  Go to settings, then advanced.  You should have a tab with the name of your card(Mine says 6800GT)  Click that then you should see NVRotate somewhere within the menus.
If that doesn't work, I feel quite sure it's in those settings(advanced settings) somewhere.  Some computers even have the option on the taskbar(by the clock)
Good luck, and be more careful next time ;P