By pressing these four keys simultaneously, you are, in a sense restarting the graphics driver. This action occurs by way of the Desktop Window Manager (DWM), which gets reset, and in turn resets the graphics driver.
The beauty of this fix is that you can perform it without having to close any applications. That being said, you should probably save any work in progress, as a failsafe, before you proceed.
Take note, this fix is only applicable to a software issue. If your monitor’s issues are hardware related — originating with the monitor itself or a failing GPU, or owing to some larger system crash — this hotkey won’t solve your problem.
You’ll know the driver has been restarted by a beep or a brief flicker on the screen. The display should now run smoothly again.