Restart
It's amazing what a simple restart will fix. Especially if you rarely turn off your Mac, sometimes little things may start acting a bit quirky. Perhaps your Mac can't find the printer you've been using for months, or icons for new files don't appear. For little unexplainable things, restart.
To restart, go to the Apple menu and choose “Restart….”
If for some reason you can't get to the Apple menu, try the Restart button that is on most Macs. It's a tiny little round button with a triangle on it.
On laptops, you can press the Power button for one second and you'll get a little message with a button to restart.
If you can't restart, then Shut Down. Either use the Apple menu command, if you can, or as a last resort hold down the Power button ...
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