If you've got Intel graphics, I think the key combination you need is Alt+Shift+UpArrow. That's from memory, though - you might need some other combination of Ctrl, Alt and/or Shift together with the up arrow key.
I don't know whether this key combination works with any other drivers, though. You might just have to poke around in the graphics options and look for "Rotation".
(Great fun can be had with this feature on other people's computers... Not that an IT professional like me would ever do anything so childish to a co-worker )
If it is an Intel integrated graphics chip and driver (for Windows) there is usually a Intel Icon on the system tray, with option to re set rotation. (you can then disable hot keys to prevent this happening again)
Sometimes you have to physically rotate screen (or stand on your head) to read the info