When you suddenly rotated your Vista Screen...
Ok, so I just did it again... and don't know how to put it back... orz
In Vista, when you suddenly put your screen rotated by pressing some key-combination that you don't even know, here is the answer...
In Vista when you want to rotate your screen, use Ctrl + Alt + Cursor key combination...
I might just pressed Ctil + Alt + → that I didn't even notice so my screen just became portrait and didn't know how to put it back. later found the answer and by press Ctrl + Alt + ↑, it came back landscape...
Last time when I encountered this situation, I re-installed my video drivers... *sigh*