Open a Finder window Select Preferences and the General tab Make sure the box next to External disks is checked.
Here are the steps: Step 1 Question: Q: External hard drive not mounting Mac After upgrading from OS X Sierra to OS X High Sierra on my MacBook Air, I can no longer mount and read my external hard drive.
When an external hard drive becomes inaccessible or unrecognized on your Mac computer, check it in Disk Utility. If you’ve found that your previously reliable external hard disk drive or SSD starts ejecting itself, trouble is obviously afoot.
