12 Replies Latest reply: Aug 3, 2007 10:36 PM by myhighway
Barefootman Level 1 Level 1 (0 points)
I've had my Mac for a year now and I love it. However, today it started switching itself off for no obvious reason. It doesn't follow any shut down sequence. It's running and then it's off as if the power's been cut. At first I thought that's what it was!

It's happened three times today. All three times it's been not running any software. I've run the software Maintainence and that didn't pick anything up.

Can anybody think where I can start looking to see what the problem might be?

iMac Intel Core Duo, Mac OS X (10.4.9)
  • myhighway Level 5 Level 5 (7,270 points)
    Run the Apple Hardware Test (AHT) that was included on your grey-labeled install discs. It should be noted on the label of the disc that contains it, although it's usually Install Disc 1. Before booting from the disc, open and read the Read-Me.
  • Matt-Beasley Level 1 Level 1 (25 points)
    Also try to fix the Hard Drive with Disk Utility, it could be that.
  • Barefootman Level 1 Level 1 (0 points)
    Also try to fix the Hard Drive with Disk Utility, it
    could be that.


    I've now tried that and so far so good. However, if I shut the computer down and then press the power button - on the back - to start it up nothing happens. I have to unplug the computer from the power source, plug it back in and then press the power button to get the computer to start up.

    I found that very strange. Any ideas on why this would be?
  • deedho Level 2 Level 2 (190 points)
    I am not having the shutdown problem, however, I find that about 50% of the time when I turn my iMac on with the power button, I have to press the button twice for it to power up. You might try that before the unplugging method.
  • Barefootman Level 1 Level 1 (0 points)
    Run the Apple Hardware Test (AHT) that was included
    on your grey-labeled install discs. It should be
    noted on the label of the disc that contains it,
    although it's usually Install Disc 1. Before booting
    from the disc, open and read the Read-Me.


    I ran the AHT and it found nothing wrong with the computer. I also ran the Disk Utility program and it found no problems.

    Do you think reinstalling OSX is the way to go?
  • Charles Minow Level 6 Level 6 (9,190 points)
    Hi--

    I've now tried that and so far so good. However, if I
    shut the computer down and then press the power
    button - on the back - to start it up nothing
    happens. I have to unplug the computer from the power
    source, plug it back in and then press the power
    button to get the computer to start up.


    There are two things you should look at. One would be to try resetting the SMC (System Management Controller) by shutting the computer off (from the Apple menu). Once it's all off, remove all the cords connected to the computer, including keyboard, mouse, power, etc., etc. Wait at least 15 seconds, then plug in the power (but make sure the power button is NOT being pressed), then the keyboard and mouse, then restart and see how it works. This article has more details.

    Second, depending on how old your computer is, you may need a firmware update. Apple's Knowledgebase has an article about it, with a link to the download page.

    I found that very strange. Any ideas on why this
    would be?


    Since unplugging the power cord works, it sounds like you're already re-setting the SMC, so definitely see if it needs the SMC update.

    charlie
  • myhighway Level 5 Level 5 (7,270 points)
    I ran the AHT and it found nothing wrong with the
    computer. I also ran the Disk Utility program and it
    found no problems.

    Do you think reinstalling OSX is the way to go?


    Well, that will certainly tell you if the problem is software or hardware, but that would be a bit premature.

    First, let me ask if your firmware is up-to-date? Your iMac's utility "System Profiler" in its "Hardware Overview" should be showing:

    Boot ROM Version: IM41.0055.B08
    SMC Version: 1.1f5

    If you don't see the same reports, it probably needs one of these two updates:

    http://docs.info.apple.com/article.html?artnum=303903

    Your symptoms sound as if your iMac might not have the updated SMC firmware installed. According to Apple: "The SMC Firmware Update addresses boot issues with the iMac."

    It's an extremely tiny update - takes about five seconds or less to download, but the installation requires caution, and strictly following the procedure will be necessary to avoid spending hours trying to correct any error you might make.

    Remember, when you are quitting your open applications after downloading, but prior to installation - AirPort is an application and needs to be turned off. Only Finder and Dashboard should have a triangle next to their Dock icons during the installation of either of the firmware updates. You may very well have applications installed whose icons are not represented in the dock, so make sure everything gets quit prior to doing the install.

    If your iMac happens to need both updates, it would be a mistake to try to do them at the same time. Once completed successfully, the update software packages can be deleted, as that's strictly a one time install - it's not software and can't be erased.

    If the SMC firmware update is needed, after successful completion, you will need to reset the SMC, which is not done as part of the installation.

    If it turns out you do not need either update, you should perform a PRAM reset to see if that might resolve your problem. To reset the PRAM:

    1. Shut down the computer.
    2. Locate the following four keys on the keyboard: Command (Apple logo), option, P, and R. You will need to hold these four keys down simultaneously in step 4.
    3. Start up the computer.
    4. Press and hold the Command-option-P-R keys. You should press this key combination immediately after the startup chord sounds, and certainly before the gray screen's Apple logo appears.
    5. Hold all four keys down until the computer restarts and you hear the startup chord for the second time. The PRAM reset will reset your sound level preference, so the second time may well sound more or less loud than the first.
    6. Release the keys.

    A second preference that's usually reset by this procedure is the Startup Disk preference. Let us know if you make any progress with your spontaneous shutdown problem.
  • Simon69 Level 1 Level 1 (30 points)
    Assuming you try everything else, and it does not work, is your Mac getting really hot ? how hot is the room you're using it in ?

    I'm wondering if it is just be shutting off because it is too hot.

    It may of course simply be a fault with the power supply in the Mac, which would be consistent with having to completely remove the power before the machine will boot.
  • isucyclones94 Level 1 Level 1 (0 points)
    I just finished reading the June 2007 edition of Macworld magazine and they have your problem featured! Here is an excerpt:
    "Fred Morris never had a problem with his Macs-not with his Mac Plus or his Special Edition iMac. But seven months after his 2006 purchase of a 20-inch iMac Core Duo, the machine began acting up. It shut down spontaneously. For a while, things would be fine after a reboot. But then the shutdowns started coming with greater frequency-every four or five days. A couple of trips to the Apple Store led to the replacement of the iMac's power supply and main logic board. But that didn't stop the shutdowns. Morris turned to AppleCare's support line, asking for a replacement iMac. Two days later, a FedEx shipping label and a box arrived. Morris used them to return the dead iMac. Three days later, a brand new iMac-a slightly newer model-arrived in its stead." (By Dan Miller)
    So I guess there's no real solution but to ask for a replacement iMac? I'd be fine with that.


      Mac OS X (10.4.9)  
  • myhighway Level 5 Level 5 (7,270 points)
    "So I guess there's no real solution"

    Welcome to Discussions, isucyclones94!

    Of course there's a solution for a Core Duo iMac. Update the firmware and the SMC firmware, then reset the SMC.

    "The SMC Firmware Update addresses boot issues with the iMac."

    If you have an issue, why not start your own thread so that you can get some proper advice?
  • kristiecan Level 1 Level 1 (0 points)
    My iMac G4 keeps shutting down on it's own, very randomly as well. Sometimes if I unplug it and plug it back into an outlet it will restart? It has been very hot here in New York, could that have anything to do with it? Please help...
  • myhighway Level 5 Level 5 (7,270 points)
    Hello kristiecan!

    Yes, heat has always (for more than half a century now) had a big impact on the operation of all computers. You can easily verify if that is the cause of your issue by transferring your iMac to a significantly cooler environment (below ground level; or air-conditioned room) to see if it works the same, or better. While that might not solve your problem, at least you'll be able to determine whether or not it's a heat-related issue.