If you see your external hard drive but receive the 'Corrupt Disk' error, solutions are plentiful. Your first issue may be that the external hard drive isn't formatted properly to work with your Mac. You can reformat the external drive using Disk Utility. 1. Simply follow the instructions above to access the drive and click on Erase (yes, you need to erase the drive to reformat it). 2. Click on the dropdown for format and select ExFat, and click Erase. Now your external hard drive should appear properly.