And sometimes, a pop-up tells you to format external hard drive on Mac because it is corrupted or virus attacked. If you want to start up again from the disk you just erased, select Reinstall macOS in the utilities window, then click Continue and follow the onscreen instructions to reinstall macOS.Sometimes when you connect your external hard drive with Mac, only to find it does not work at all.After your Mac activates, click Exit to Recovery Utilities.Use the Wi-Fi menu in the menu bar to choose a Wi-Fi network, or attach a network cable. Your Mac now attempts to activate, which requires an internet connection.When your Mac restarts, follow the onscreen instructions to choose your language.When asked whether you're sure you want to erase this Mac, click Erase Mac and Restart.Click Erase. However, if you see an Erase Volume Group button, click that button instead.Click the Erase button in the toolbar, then specify a name and format:.Now select Macintosh HD in the sidebar.

If you previously used Disk Utility to add volumes to your startup disk, select each additional internal volume in the sidebar, then click the delete volume (–) button in the toolbar to delete that volume.ĭuring this step, disregard any internal volume named Macintosh HD or Macintosh HD - Data, as well as any volumes in the External and Disk Images sections of the sidebar.In the Internal section of the Disk Utility sidebar, make sure that you see the volume named Macintosh HD.From the utilities window, select Disk Utility and click Continue.If asked, enter the Apple ID and password previously used with this Mac.If asked, select a user you know the password for, then enter their administrator password.Turn on your Mac and continue to press and hold the power button until you see the startup options window.

Format hard drive in mac