Hello,
After my son aged 8 finished using the computer the screen display was rotated 90 degrees. He was playing an on line game.
I have been into the control panel and then display but nothing seems to rotate the display back and my neck is now hurting.
The computer is a Dell Dimension 3000 with old style monitor, operates with windows XP

If it is an Intel board with onboard video, these hotkeys may work:

• <Ctrl> + <Alt> + <Right Arrow>
• <Ctrl> + <Alt> + <Down Arrow>
• <Ctrl> + <Alt> + <Left Arrow>
• <Ctrl> + <Alt> + <Up Arrow>

If it has a Nvidia video card, there may be an icon in the system tray (next to to the clock in the lower right) that you can right-click and change the monitor settings. You'll be looking for "Rotate" or "Rotation"