Go to 'System Preferences' > 'Keyboard & Mouse' > 'Keyboard Shortcuts' > check whether the shortcuts are activated or not under Screen Shots, and also check that they have not been assigned to something else. You can use the shortcuts Command + Shift + 3 to capture a full-screen screenshot and Command + Shift + 4 to take a selected region unless you have activated the shortcuts. Press 'Control + Command + Eject' (or 'Control + Command + Power' button).

Choose the 'Apple key' and then click 'Restart'.Press the Power button (or press 'Control + Eject') and, when a dialog box appears, click the Restart button.Long-time no restarting your Mac may cause some applications won't work well. Don't worry, fix it following methods below. Many users have found the command shift 4 not working on Mac when they want to take a screenshot of a selected area and no camera shutter or no image saved on Mac. 4 effective tips to fix screenshot not working on Mac Then, how to fix this issue timely and continue with a screenshot on Mac? Read on to get effective tips. However, many users have reported that they have met the Mac screenshot not working problem like said above without any specific reason. Theoretically speaking, it's easy to take a screenshot on Mac when there is no matter going on. I hear the camera shutter sound but they are not appearing on my desktop and when I search for any images created today on my Mac, they are not there. Does anyone know how to fix this?” - A user from Apple Discussions “The shortcuts for the screenshot on my MacBook Pro are not working.

Mac screenshot command