Try this:
Some computers can rotate the Windows display by 90° or 180°. It can be disconcerting when activated by a mistaken key press. In most cases, holding down Control and Alt before tapping one of the cursor (arrow) keys will fix the problem – the up and down arrows flip the display vertically, the left and right arrows flip it horizontally.
If that fails, in Windows 7, press the Windows key and R, type desk.cpl and press Enter. Press Alt and O, then use the up and down arrow keys to select Landscape. Press Alt and A to apply, then click Keep Changes.
GB in Wales, February 2013