IMAC 27 Inch (Mid 2011) keeps restarting halfway through booting up

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Level 1

11 points

IMAC 27 Inch (Mid 2011) keeps restarting halfway through booting up

Since installing the most recent IOS Yosemite update the IMAC 27 inch (Mid 2011) keeps restarting.

Had initially rebooting and resintalled twice with the Apple Key and R held down

System would work for a while then randomly restart and thought maybe something with the Graphics Card

Now whenever trying to start up to try to run some initial Mac Apple Diagnostics cannot get IMAC to completely start up before it reboots.

Any assistance would be greatly appreciated.

Thanks

B

iMac (27-inch Mid 2011)

Posted on Mar 10, 2015 7:11 PM

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Answer 1

Kappy

Level 10

361,741 points

Mar 10, 2015 7:14 PM in response to Beckstarco

Try these in order testing your system after each to see if it's back to normal:

1. a. Resetting your Mac's PRAM and NVRAM

b. Intel-based Macs: Resetting the System Management Controller (SMC)

2. Restart the computer in Safe Mode, then restart again, normally. If this doesn't help, then:

Boot to the Recovery HD: Restart the computer and after the chime press and hold down the COMMAND and R keys until the Utilities 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.

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

When the recovery menu appears select Disk Utility. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU 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 DU and return to the main menu. Select Restart from the Apple menu.

4. Reinstall Yosemite: Reboot from the Recovery HD. Select Reinstall OS X from the Utilities menu, 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.

5. Reinstall Yosemite 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.

How to Clean Install OS X Yosemite

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

because it is three times faster than wireless.

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Answer 2

Beckstarco Author

Level 1

11 points

Mar 10, 2015 7:37 PM in response to Kappy

Hi Kappy

Thanks for your suggestion.

Only in the last 15 minutes have tried all the options from below, especially safe boot, AHT and Resetting NVRAM,

The same thing keeps happening in every option I try.

The apple logo appears and the grey line bar loads up until the start of the apply logo then the IMAC just restarts, no matter which option I try below, so am stuck as to what can try as a diagnosis if it will not finish a boot up, not even in safe mode.

Thanks

Keystroke	Description
Press C during startup	Start up from a bootable CD, DVD, or USB thumb drive (such as OS X install media).
Press D during startup	Start up in Apple Hardware Test (AHT).
Press Option-Command-P-R until you hear startup sound a second time.	Reset NVRAM
Press Option during startup	Start up in Startup Manager, where you can select an OS X volume or network volume to start from.
Press Eject, F12, or hold the mouse or trackpad button	Ejects any removable media, such as an optical disc.
Press N during startup	Attempt to start up from a compatible network server (NetBoot).
Press T during startup	Start up in Target Disk Mode.
Press Shift during startup	Start up in Safe Boot mode and temporarily disable login items.

Startup key combinations for Intel-based Macs - Apple Support

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Answer 3

Kappy

Level 10

361,741 points

Mar 10, 2015 7:43 PM in response to Beckstarco

Reinstall OS X as instructed. If that doesn't work continue on to erasing the drive and reinstalling OS X. If that doesn't work, then make a Genius Appointment and take it in for service.

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Answer 4

Beckstarco Author

Level 1

11 points

Mar 10, 2015 7:49 PM in response to Kappy

Thanks Kappy. Guess will need to book a Genius appointment as cannot even get to the Utilities menu when I hold down theCOMMAND and R keys until the Utilities menu screen appears.

Have tried that twice and the screen just goes white and wait holding the keys for a good 3 - 4 minutes and nothing happens. Thankyou all the same for the other suggestions.

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Answer 5

Jul 18, 2015 6:22 AM in response to Beckstarco

It is caused by the AMD Radeon 6970M Video Card, try iMac (27-inch): AMD Radeon 6970M Video Card Replacement Program - Apple Support

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