iMac not loading past loading screen after power outage

Reinstalling OS X Without Erasing the 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.

Repair the Hard Drive and Permissions: Upon startup select Disk Utility from the main menu. Repair the Hard Drive and Permissions as follows.

When the recovery menu appears select Disk Utility and press the Continue button. After Disk Utility loads select the indented Macintosh HD entry from the the left side list. Click on the First Aid tab, then click on the Repair Disk button. If Disk Utility reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit Disk Utility and return to the main menu.

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

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

Alternatively, see:

Reinstall OS X Without Erasing the Drive

Choose the version you have installed now:

OS X Yosemite- Reinstall OS X

OS X Mavericks- Reinstall OS X

OS X Mountain Lion- Reinstall OS X

OS X Lion- Reinstall Mac OS X

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

if possible because it is three times faster than wireless.

The hard drive may have been damaged during the outage. If so that may simply require reformatting the drive or, worst case scenario, replacing the drive.

The procedure I posted does not erase the drive or your data.

If you already purchased Mountain Lion from the App Store then you can re-download the installer via your Purchases page in the App Store. To download through what you are trying requires the Apple ID used to purchase Mountain Lion. Otherwise, there may actually be a problem on Apple's end. Are you sure you didn't try to download Mavericks? You were able to boot from your Recovery HD and you do have Mountain Lion currently installed?

Use OPTION boot to startup from the Mountain Lion disk:

Boot Using OPTION key:

1. Restart the computer.

2. Immediately after the chime press and hold down the

"OPTION" key.

3. Release the key when the boot manager appears.

4. Select the Mountain Lion installer disk.

5. Click on the arrow button below the icon.

Appologies I've got nothing to add that would help, but I'm having almost exactly the same issue.

We had a power cut whilst my iMac was in sleep mode. It began feeling really slow and eventually froze completely. I closed it down by holding the power button. Tried switching it on and it hangs on the loading screen at around 30% or 50%. I tried opening in safe mode but it didn't seem to work either, it still hangs.

So I unplugged it to reset the SMC and also tried holding Apple option R and P as this was suggested on another forum but that didn't help. So I opened in recovering mode and tried repairing the hard drive which I was able to do, but it didn't help. So I then tried recovering mode again and reinstalled the OSX. This took 18 hours to complete! But when the computer restarted, the same issue happend and it hangs on the boot up screen.

Now it won't even let me open recovery mode. I didn't know if this is because after reinstalling the OS X, it's not recognising my wireless keyboard.

But at this stage I think taking it to a repair shop is my only option.

A normal system reinstall shouldn't take over an hour, so you needed to reinstall from scratch. I hope you have a backup.

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.

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 that you had installed.

Yes. I did the reinstall but it still won't boot up. And now command R doesn't work either.

I do have a time machine so I'm still hopeful I'll be able to get everything back, if I could just get it to boot up.

Do you mean you installed OS X from scratch? Or are you referring to the 18 hour reinstallation?

You should be able to boot from your Time Machine backup drive using OPTION boot:

Boot Using OPTION key:

1. Restart the computer.

2. Immediately after the chime press and hold down the

"OPTION" key.

3. Release the key when the boot manager appears.

4. Select the disk icon for the Time Machine disk's Recovery HD.

5. Click on the arrow button below the icon.

Then proceed as outlined above.

The 18 hour reinstall.

I've just removed the third party ram as I'd heard this sometimes causes issues. Though it hasn't changed anything.

I've also tried to reinstall from the OS X disc. Mine is a mid 2011 iMac. But holding C doesn't seem to work either.

Pressing the the option key after the chime doesn't work either. I'm still just getting the boot up screen and the black progress bar which hangs at 50%

I believe your hard drive has failed. Apparently, the optical drive isn't working either or your Snow Leopard DVD needs cleaning (it is the one that came with the computer, isn't it?)

This is probably the case. When I take it to the Apple Store. Would you suggest I also take the time machine?