Hi
If you mean that the screen has flipped sideways.
Right click on the desk top and see if you have an option called Screen Resolution.
Find the box that is labeled Orientation.
Change it to Landscape.
If you don't have that option...
Right click on the desktop and select Personalize.
Then Click Display.
Next Click Change Display Settings.
Find the box that is labeled Orientation.
Change it to Landscape.
Holding you mouse sideways may make this easier.
Alternately you may have a link to your video card software on the right click drop down from the desktop.
Mine is Catalyst Control Center, if I go there I can change the Orientation as well.
Mike