PC question, monitor display is vertical, should be horizontal

[SweetHomeColorado]

I'm not sure what happened, I may have pressed incorrect keys in succession, but my monitor flipped from the standard view to everything being on it's side. I had to turn my monitor on it's side.
When I start the PC, the display is normal, only after windows loads does the display switch to it's side.

What did I do and how can I fix it? This is such an annoyance!

[St_Ides]

I seem to recall the old shortcut on my ATI video card was CTRL + ALT + (Arrow key left or right, depending on which direction you want it rotated)

My Nvidia doesn't appear to have that option.

[SweetHomeColorado]

and circle gets the square!
That did it! thanks!

[Mangetout]

Link (http://boards.straightdope.com/sdmb/showthread.php?t=435646) (just for the sake of more information) to recent thread on the topic.