I've worked with flat-screen panels that can be rotated 90 degrees to portrait mode, and the laptop has additional screen driver software that rotates the display 90, 180, 270 degrees.
Perhaps you have something similar installed? It could be in the graphics card properties, perhaps.
On my PC I have an NVIDIA tab on display properties (for the venerable GeForce 2 MX card) that allows me to rotate the screen.
If all else fails, sell it to an Australian.
SD