How to Reboot an Apple iMac to Its Factory Settings

Verify that your iMac is connected to the Internet, click the Apple menu in the upper-left corner of your screen, and then select 'Restart.'
Press and hold 'Command-R' when the iMac gets to the gray screen during the restart process.
Select 'Disk Utility,' and then click 'Continue.'
Click your hard drive on the list of hard disks, and then click the 'Erase' tab.
Click the 'Format' pop-up menu and select 'Mac OS Extended (Journaled).'
Enter a name for your hard drive, and then click 'Erase' to erase its contents. The name you enter is what your hard drive will be called after the reformatting process is complete.
Click 'Disk Utility,' and then click 'Quit Disk Utility' once the hard drive has been erased.
Select 'Reinstall OS X,' and then click 'Continue.'
Follow the on-screen prompts and, when you arrive at the Disk Selection pane, select the hard disk you named in Step 7.
Click 'Install' to reinstall the OS X operating system.
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