You might want to check to see if you have a virus. Be sure you antivirus
software has the latest definitions.
Usually, this sort of thing controlled on the monitor by the way so you
might want to check your manual to see if there is a control for such a
thing. For example, some flat panel monitors can display an image
horizontally or vertically or it might be called landscape or portrait,
nonetheless, if your monitor falls into that category, hitting the wrong
control would appear to put the image on its side but as I said above, you
might want to virus scan first.