Article intended to fix an issue where MAC devices aren't registering screen shots or allowing screen capture. Restart the computer.  Running a Mac for long periods without shutting it down can cause it to perform inefficiently or prevent certain apps from working properly. If the screenshot feature on your Mac isn't working, shut down the Mac and turn it on again.  Then take a screenshot according to your preferred method, whether that's the keyboard shortcut or the Screenshot app. Check the screenshots keyboard shortcuts.  These settings are on by default.  They may have been switched off at some point or set to keyboard combinations other than the defaults. To check this, go the System Preferences > Keyboard > Shortcuts.  There you can see whether keyboard shortcuts have been turned off or reassigned to other actions. Reset the NVRAM.  Like a simple restart, resetting the non-volatile random-access memory (NVRAM) can sometimes resolve issues with core Mac apps and functionality. This memory is responsible for controlling many of the internal settings of the computer. The process to reset the NVRAM can be a little confusing, so additional instructions for that are listed at the bottom of this article. Confirm the location for saving screenshots in the Screenshot app.  The default is to save screenshots to the Desktop.  If you changed that setting, your screenshots may be hiding somewhere you haven't looked.  Check the location on the Screenshot app's floating menu bar. The NVRAM affects a vast majority of items on Mac devices and may need reset for multiple reasons.  While this shouldn't be a common solution to run through, it is important to know how to do it.  Instructions for the reset are listed below. Shut down your Mac. Turn your Mac back on. Immediately press and hold the following keys: command+option+P+R. That's four keys: the command key, the option key, the letter P, and the letter R. You must press and hold these four keys before you see the gray screen during the startup process. Continue to hold down the four keys. This is a long process, during which your Mac will restart on its own. Finally, when you hear the second startup chime, you can release the keys. Your Mac will finish the startup process.

Symptoms:   1. After docking your Macbook or connecting an external monitor there is no picture on the external monitor. 2.  The external monitors are not showing in System Preferences (Settings) under Display. Solution: Ensure that the DisplayLink Manager software is running and that the option to "Launch automatically after login" is checked. Run the DisplayLink Manager: - Go to Spotlight - Type DisplayLink Manager and press Enter (if you do not have this installed, it is under the Targus - DisplayLink heading in Self Service. - On the menu bar, click the DisplayLink Manager icon. - Check the box for Launch automatically after login.