did you accidentally hit a button on your monitor???
or did you try to alt-ctrl-delete and miss??
try this;
My screen is sideways
Q. I attempted to press CTRL + ALT + DELETE to bring up the task menu but must have inadvertently pressed a different key combination. Now the display on the screen is horizontal (from left to right) rather than vertical (top to bottom).
A. Some video cards support the rotation of the image on your computer screen. You'd use this if you a monitor that can also rotate. Web designers and artists use this, as an example, to check long pages.
It would appear that you managed to press CTRL + ALT + Left Arrow.
To correct this problem simply click CTRL + ALT + Up Arrow.