In most operating systems, there is an option to rotate the screen so that an external monitor can be installed. However, if a user activates this feature on the main screen, this could cause problems turning the screen upside down or on its side. You can use menu options or keyboard shortcuts to fix this problem.
Quick solution

Steps
Method 1 of 2: On Windows

Step 1. Press "Ctrl", "Alt" and one of the arrows
On some graphics cards, the key combination Ctrl + alt = "Image" + ↓ is designed to turn the screen upside down. So press Ctrl + alt = "Image" + ↑ to reverse it. If the screen was turned left or right, you can use this same key combination by replacing the last key with ← or → to reverse it.
- On other graphics cards, the key combination used is ⇧ Shift + alt = "Image" + ↑.
- You may have to press the "Alt" key on the right side of the space bar, which is sometimes called AltGr.

Step 2. Manually fix the screen rotation
In Windows 7 operating systems onwards there is an option to change the screen from portrait to landscape mode. To fix it, follow the steps below:
- Right click on the Desktop.
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Select the Show settings (for Windows 10) or Screen resolution (for Windows 7 or 8) option from the drop-down menu that appears.
(Another option is to go to Start → Control Panel → Display and then choose the Display Settings or Screen Resolution option).
- Click on the "Orientation" drop-down menu and change the option to "Portrait" or "Landscape" depending on how the screen is configured.
- Click "Apply" to return the screen to its original orientation.

Step 3. Access your graphics card options
In case no other method works, you will have to access the graphics card settings. This could be labeled "Graphics Options", "Graphics Properties", "NVIDIA Control Panel", "Catalyst Control Center" or "Intel Control Center" depending on your particular graphics card. To find this menu, you can either use the search bar or right-click on the Desktop and select the corresponding option from the drop-down menu (which is usually the most common).

Step 4. Change the rotation settings
There is no standard layout in the graphics card menus, so this could cause you to have to do a bit of searching. The settings for "Rotation" or "Orientation" are usually found in the "Display Manager" menu on some graphics cards.
- To find these settings, you may have to choose "Advanced Options".
- If you're not sure about the reasons why the screen rotated, it could be because you accidentally pressed a keyboard shortcut. So find an option from a shortcut menu and turn it off.
Method 2 of 2: On Mac

Step 1. Hold down the "Command" and "Option" keys
Hold down the Command and Option keys and continue in this manner for the rest of this process.
If your Mac uses a Windows keyboard, you must press the Ctrl + Alt keys

Step 2. Open "System Preferences"
Click on the Apple symbol in the upper left corner of the screen and choose System Preferences from the drop-down menu that appears.
If this option was already open, you may have to exit and reopen it but this time keeping the aforementioned keys pressed

Step 3. Go to the screen settings
Click Display while holding down both keys.
If there is more than one screen, you must choose the one with which you have the problem from the list of options before continuing

Step 4. Change the rotation settings
Holding down both keys activates the rotation options within the "Display" settings. To return the screen to its original settings, choose the Standard option from the "Rotation" drop-down menu.