right-click on an empty area on the desktop, click on 'properties' then on the 'settings' tab followed by the 'Advanced' button. On here there is a tab relating to graphics, mines a Geforcefx card so on the tabs its that, then on list on the left look for nv rotate check should be in landscape 0 degree rotation
On some types of graphics cards you can also rotate the screen by holding Ctrl/Alt and pressing the up/down arrows or left/right if you want a sideways view best bet is keep the kids off the comp they know more than us lol