It would sure help if you could tell us more about your computer.. The operating system, laptop or desktop? Make and model? etc.
In the meantime, rotating the monitor display is done from within the graphics console options. As you described, sometimes, you can press the Ctrl+Alt+ "up arrow key" as a shortcut key to the process..
There may also be a graphics icon in your lower right corner system tray.. If that's the case, check the "Rotation settings" by RIGHT clicking on the icon. Choose the "No rotation" or "0 degrees" option if they are there..
If neither of the above help, then open the Control Panel, double click on the graphics icon (for example, Nvidia has an "nVidia Control Panel"), then select the "Rotate Display" options.
Hope this helps.
I am not a computer geek, nor my wife! Last night she did something to make the image on our monitor turn 45 degrees. How do I get it to go back to normal? I tried ctrl alt and arrows but no luck!