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"