iMac Boot Loop?

1. You could have failing RAM.
2. Your HDD may need replacing.
3. You may just need to erase the drive then reinstall OS X:

Install or Reinstall OS X from Scratch

Be sure you backup your files to an external drive or second internal drive because the following procedure will remove everything from the hard drive.

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

Erase the hard drive:

1. Select Disk Utility from the main menu and click on the Continue button.

2. After DU loads select your startup volume (usually Macintosh HD) from the

left side list. Click on the Erase tab in the DU main window.

3. Set the format type to Mac OS Extended (Journaled.) Optionally, click on

the Security button and set the Zero Data option to one-pass. Click on

the Erase button and wait until the process has completed.

4. Quit DU and return to the main menu.

Reinstall OS X: Select Reinstall OS X and click on the Install button.

Note: You will need an active Internet connection. I suggest using Ethernet if possible

because it is three times faster than wireless.

This should install the version of OS X you were running.

If Lion or later is installed, then there is a Recovery HD. Have you tried booting from it?

I don't recall you stating you had a blank HDD. You can do an Internet Recovery. Please check this out: Computers that can be upgraded to use OS X Internet Recovery. After installing the firmware update you can use Internet Recovery.

If your HDD is actually blank and has never had OS X installed, then you must begin by installing from the Snow Leopard DVDs that came with the computer when it was new. After you install Snow Leopard then you can download Lion or later from the App Store.

Clean Install of Snow Leopard

1. Boot the computer using the Snow Leopard Installer Disc or the Disc 1 that came

with your computer. Insert the disc into the optical drive and restart the computer.

After the chime press and hold down the "C" key. Release the key when you see

a small spinning gear appear below the dark gray Apple logo.

2. After the installer loads select your language and click on the Continue

button. When the menu bar appears select Disk Utility from the Utilities menu.

After DU loads select the hard drive entry from the left side list (mfgr.'s ID and drive

size.) Click on the Partition tab in the DU main window. Set the number of

partitions to one (1) from the Partitions drop down menu, click on Options button

and select GUID, click on OK, then set the format type to MacOS Extended

(Journaled, if supported), then click on the Apply button.

3. When the formatting has completed quit DU and return to the installer. Proceed

with the OS X installation and follow the directions included with the installer.

4. When the installation has completed your computer will Restart into the Setup

Assistant. After you finish Setup Assistant will complete the installation after which

you will be running a fresh install of OS X. You can now begin the update process

by opening Software Update and installing all recommended updates to bring your

installation current.

Download and install Mac OS X 10.6.8 Update Combo v1.1.

When you got to the Internet Utilities panel did you run Disk Utility and partition and format your new hard drive? It must be prtitioned using the GUID scheme and formatted as Mac OS Extended Journaled.

Install OS X Using Internet Recovery

Boot to the Internet Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND-OPTION- R keys until a globe appears on the screen. Wait patiently - 15-20 minutes - until the Recovery main menu appears.

Partition and Format the hard drive:

1. Select Disk Utility from the main menu and click on the Continue button.
2. After DU loads select your newly installed hard drive (this is the entry with the mfgr.'s ID and size) from the left side list. Click on the Partition tab in the DU main window.
3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Options button, set the partition scheme to GUID then click on the OK button. Set the format type to Mac OS Extended (Journaled.) Click on the Partition button and wait until the process has completed. Quit DU and return to the main menu.

Reinstall OS X: Select Reinstall OS X and click on the Install button. Be sure to select the correct drive to use if you have more than one.

Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.

This should restore the version of OS X originally pre-installed on the computer.

You NEED to partition and format your new hard drive.

You CANNOT install OS X on a bare unformatted and unpartitioned hard drive. I never said anything about a recovery drive. I said when you get booted into Internet recovery to use Disk Utility and partition and format. Until you do that you cannot proceed. THEN reinstall Os X after formatting and partitioning. Follow Kappy's instructions.

DarraghQ wrote:

The Internet Recovery does show up, but just fails mid-way. I tried to install Mavericks onto the new HD by using a USB, but once again, it failed mid-way and restarted.

I took this to maen that you DID make it to IR but the install failed. Your imac shipped with install discs correct? You need those and go back to Kappy's instructions on how to do a clean install of Snow Leopard above. You still need to format and partition but now you'll be running DU from your install discs.