If your external hard drive isn’t detected once you’ve plugged it in, usually you’ll just need to make a few changes in “Preferences.” However, occasionally the problem can be more severe, like a short power supply. Try the following to get your external hard drive to show up in Finder: 1. Go to the “Finder” menu, then click “Preferences.” 2. From “General,” select “External disks” to ensure that it shows on the desktop once you connect an external drive. From the sidebar tab, you can select which folders and devices to display in the left-hand column of the “Finder” window.