Owners of the Apple iMac can restore the computer to factory settings by erasing and reinstalling the operating system from the Mac OS X Install DVD. The process of restoring the computer consists of four steps. These steps include erasing the hard drive, installing Mac OS X, completing the setup assistant and reinstalling the software bundled with the iMac.
Erase Hard Drive
Insert the Mac OS X Install DVD into the iMac optical drive with the computer running. Restart the iMac and hold the "C" key while the computer restarts. This forces the computer to start up from the DVD.
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Select the language when prompted and press the "right arrow" key to continue. Click "Utilities" in the menu bar and select "Disk Utility."
Click "Macintosh HD" in the Disk Utility window and select the "Erase" tab. Click "Erase" to erase the hard drive. This process completely deletes all applications and files stored on the computer. Be sure your data is backed up before erasing the hard drive.
Click "Erase" when promoted to confirm the selection. After the process is complete, click "Disk Utility" in the menu bar and select "Quit Disk Utility" from the drop-down menu.
Install Mac OS X
Click "Continue" when the Mac OS X installer screen appears after quitting "Disk Utility." Click "Agree" after reviewing the licensing agreement.
Select "Macintosh HD" as the location for the operating system to be installed and click "Install" when prompted.
Click "Continue" at the information screen indicating the installation is complete. Click "Restart" at the next screen to restart the computer.
Complete the Setup Assistant
Select the appropriate country or region and click "Continue" after the computer restarts and the welcome video finishes. Select the desired keyboard layout and click "Continue."
Choose if you wish to import your data at this time from an external backup hard drive. To restore your iMac to factory settings, the data should be restored at a later time. Click "Continue" once the selection is made.
Enter the information for your wireless network if you wish to connect at this time. The information includes the network username and password. Click "Continue."
Create an Apple account at the Apple ID screen if desired. The account is used to purchase content in the iTunes store and is not required. Click "Continue."
Enter a username and password at the Create Your Account screen to create your iMac user account. Click "Continue" to create the account. Select a picture for the account and click "Continue."
Enter your MobileMe information if applicable and click "Continue." Click "Go" to finish the setup process, and eject the Install DVD by dragging the CD icon to the Trash.
Install Bundle Applications
Insert the Applications Install Disc into the iMac optical drive. Double-click the "Install Bundled Software" icon and click "Continue" when prompted. Click "Agree" after reviewing the software licensing agreement.
Select the "Macintosh HD" for the installation destination. Follow the on-screen directions to proceed with the installation. Enter your account password created earlier if prompted.
Click "Continue" once the installation is complete and you are prompted to restart the computer. Eject the Application Install Disc after the computer restarts.
Erasing the hard drive is permanent and cannot be undone. Be sure all your data is backed up before beginning this process.