Q: Why is my imac shutting down by itself?

The good news continues the desk lamp is off my IMac keeps going, day three and counting

I have a refurb 27-inch 4.0GHz 5k iMac. Beautiful machine. But while booted into os X it will shut itself down. BUT, and I think a large but, is that I've been booted into Windows 10 via Bootcamp for weeks. And no shutdown for weeks, works just as it should, goes to sleep, sometimes for a long time, and will wake up nicely with a tap of the keyboard. So I think it's definitely a software issue. I haven't waded through all the posts but I thought I'd offer this to folks that are following the hardware side. Not that it isn't a possibility to some, but not all I'd guess.

Reporting in and again good news no shut down, my lamp which was right next to my mac is off and no problems, i am beginning to believe that in my case it was the heat from the lamp that was shutting down my mac so remove any lights near your screen and give it a go

Hi I'm not sure if I am posting in the correct place but I have a similar problem, Imac 27 inch mid 2010 recent replacement hard drive etre check below, any guidance would be very much appreciated

EtreCheck version: 2.9.12 (265)

Report generated 2016-05-26 09:05:58

Download EtreCheck from https://etrecheck.com

Runtime 2:09

Performance: Excellent

Click the [Support] links for help with non-Apple products.

Click the [Details] links for more information about that line.

Problem: Computer is restarting

Hardware Information: ⓘ

    iMac (27-inch, Mid 2010)

    [Technical Specifications] - [User Guide] - [Warranty & Service]

    iMac - model: iMac11,3

    1 3.2 GHz Intel Core i3 CPU: 2-core

    8 GB RAM Upgradeable - [Instructions]

BANK 0/DIMM0

2 GB DDR3 1067 MHz ok

BANK 1/DIMM0

2 GB DDR3 1067 MHz ok

BANK 0/DIMM1

2 GB DDR3 1067 MHz ok

BANK 1/DIMM1

2 GB DDR3 1067 MHz ok

Bluetooth: Old - Handoff/Airdrop2 not supported

Wireless:  en1: 802.11 a/b/g/n

Video Information: ⓘ

    ATI Radeon HD 5670 - VRAM: 512 MB

        iMac 2560 x 1440

System Software: ⓘ

    OS X El Capitan 10.11.5 (15F34) - Time since boot: about one hour

Disk Information: ⓘ

    WDC WD10EZEX-00WN4A0 disk0 : (1 TB) (Rotational)

        EFI (disk0s1) <not mounted> : 210 MB

        Macintosh HD (disk0s2) / : 999.35 GB (830.25 GB free)

        Recovery HD (disk0s3) <not mounted>  [Recovery]: 650 MB

    OPTIARC DVD RW AD-5680H   ()

USB Information: ⓘ

    Apple Card Reader

    Apple Inc. BRCM2046 Hub

        Apple Inc. Bluetooth USB Host Controller

    Apple, Inc. Keyboard Hub

        Apple, Inc Apple Keyboard

    Apple Computer, Inc. IR Receiver

    Apple Inc. Built-in iSight

Gatekeeper: ⓘ

    Mac App Store and identified developers

Kernel Extensions: ⓘ

        /Applications/Parallels Access.app

    [not loaded]    com.parallels.virtualhid (1.0.3 - SDK 10.9 - 2015-10-28) [Support]

    [not loaded]    com.parallels.virtualsound (1.0.36 - SDK 10.6 - 2015-10-28) [Support]

        /Applications/Parallels Desktop.app

    [not loaded]    com.parallels.kext.hidhook (9.0 24251.1052177 - 2014-09-22) [Support]

    [not loaded]    com.parallels.kext.hypervisor (9.0 24251.1052177 - 2014-09-22) [Support]

    [not loaded]    com.parallels.kext.netbridge (9.0 24251.1052177 - 2014-09-22) [Support]

    [not loaded]    com.parallels.kext.usbconnect (9.0 24251.1052177 - 2014-09-22) [Support]

    [not loaded]    com.parallels.kext.vnic (9.0 24251.1052177 - 2014-09-22) [Support]

        /System/Library/Extensions

    [loaded] com.logmein.driver.LogMeInSoundDriver (4.1.5851 - 2016-05-25) [Support]

    [not loaded]    com.tomtom.driver.UsbEthernetGadget (1.0.0d1 - 2016-05-25) [Support]

Startup Items: ⓘ

    HWPortDetect_driver: Path: /Library/StartupItems/HWPortDetect_driver

    Startup items are obsolete in OS X Yosemite

System Launch Agents: ⓘ

    [not loaded]    7 Apple tasks

    [loaded] 157 Apple tasks

    [running] 74 Apple tasks

System Launch Daemons: ⓘ

    [not loaded]    46 Apple tasks

    [loaded] 154 Apple tasks

    [running] 90 Apple tasks

Launch Agents: ⓘ

    [running] com.epson.Epson_Low_Ink_Reminder.launcher.plist (2015-01-19) [Support]

    [loaded] com.epson.esua.launcher.plist (2016-03-28) [Support]

    [running] com.epson.eventmanager.agent.plist (2014-09-21) [Support]

    [loaded] com.google.keystone.agent.plist (2016-03-03) [Support]

    [loaded] com.hp.help.tocgenerator.plist (2009-07-28) [Support]

    [loaded] com.intego.backupassistant.agent.plist (2014-07-30) [Support]

    [not loaded]    com.logmein.logmeingui.plist (2016-03-03) [Support]

    [not loaded]    com.logmein.logmeinguiagent.plist (2016-03-03) [Support]

    [not loaded]    com.logmein.logmeinguiagentatlogin.plist (2016-03-03) [Support]

    [loaded] com.oracle.java.Java-Updater.plist (2012-12-31) [Support]

    [loaded] com.parallels.mobile.prl_deskctl_agent.launchagent.plist (2015-10-28) [Support]

Launch Daemons: ⓘ

    [failed] com.adobe.fpsaud.plist (2016-05-09) [Support]

    [running] com.fitbit.galileod.plist (2013-10-22) [Support]

    [loaded] com.google.keystone.daemon.plist (2016-03-03) [Support]

    [running] com.intego.BackupAssistant.daemon.plist (2014-07-30) [Support]

    [not loaded]    com.logmein.logmeinserver.plist (2016-03-03) [Support]

    [loaded] com.logmein.raupdate.plist (2013-12-16) [Support]

    [loaded] com.microsoft.autoupdate.helpertool.plist (2016-05-22) [Support]

    [loaded] com.microsoft.office.licensing.helper.plist (2013-09-13) [Support]

    [loaded] com.microsoft.office.licensingV2.helper.plist (2016-02-12) [Support]

    [loaded] com.oracle.java.Helper-Tool.plist (2012-12-31) [Support]

    [running] com.parallels.mobile.dispatcher.launchdaemon.plist (2015-10-28) [Support]

    [failed] com.parallels.mobile.kextloader.launchdaemon.plist (2015-10-28) [Support]

    [loaded] com.prosofteng.DriveGenius.locum.plist (2014-10-21) [Support]

    [running] com.surteesstudios.hddfancontroldaemon.plist (2014-06-03) [Support]

User Launch Agents: ⓘ

    [running] com.google.Chrome.framework.plist (2016-05-26) [Support]

    [loaded] com.parallels.mobile.startgui.launchagent.plist (2016-03-04) [Support]

    [loaded] com.valvesoftware.steamclean.plist (2015-09-04) [Support]

User Login Items: ⓘ

    iTunesHelper    Application (/Applications/iTunes.app/Contents/MacOS/iTunesHelper.app)

Other Apps: ⓘ

    [running] com.microsoft.Office365ServiceV2.176672

    [running] com.parallels.inputmethod.ParallelsIM.72032

    [loaded] 407 Apple tasks

    [running] 200 Apple tasks

Internet Plug-ins: ⓘ

    Flip4Mac WMV Plugin: 3.2.0.16   - SDK 10.8 (2013-09-24) [Support]

    FlashPlayer-10.6: 21.0.0.242 - SDK 10.6 (2016-05-17) [Support]

    QuickTime Plugin: 7.7.3 (2016-05-25)

    Flash Player: 21.0.0.242 - SDK 10.6 (2016-05-17) [Support]

    Default Browser: 601 - SDK 10.11 (2016-05-25)

    SharePointBrowserPlugin: 14.6.4 - SDK 10.6 (2016-05-22) [Support]

    Silverlight: 5.1.41212.0 - SDK 10.6 (2016-04-11) [Support]

    DirectorShockwave: 12.1.3r153 - SDK 10.6 (2014-06-24) [Support]

    JavaAppletPlugin: Java 8 Update 91 build 14 (2016-05-06) Check version

User internet Plug-ins: ⓘ

    Google Earth Web Plug-in: 7.1 (2013-10-07) [Support]

Safari Extensions: ⓘ

    AdBlock - BetaFish, Inc. - https://getadblock.com (2016-05-22)

    DuckDuckGo - DuckDuckGo - http://duckduckgo.com (2016-03-04)

    OneNote Web Clipper - Microsoft Corporation - https://www.onenote.com/Clipper (2016-05-22)

    Pin It Button - Pinterest, Inc. - http://www.pinterest.com/ (2016-03-04)

3rd Party Preference Panes: ⓘ

    Flash Player (2016-05-09) [Support]

    Flip4Mac WMV (2013-03-29) [Support]

    HDD Fan Control (2016-03-03) [Support]

    Java (2016-05-06) [Support]

Time Machine: ⓘ

    Skip System Files: NO

    Mobile backups: OFF

    Auto backup: YES

    Volumes being backed up:

        Macintosh HD: Disk size: 999.35 GB Disk used: 169.10 GB

    Destinations:

        LaCie [Local]

        Total size: 800.16 GB

        Total number of backups: 33

        Oldest backup: 01/03/2016, 12:28

        Last backup: 24/05/2016, 07:07

        Size of backup disk: Adequate

            Backup size 800.16 GB > (Disk used 169.10 GB X 3)

Top Processes by CPU: ⓘ

         6% Google Chrome Helper(8)

         2% Google Chrome

         2% WindowServer

         1% fontd

         0% kernel_task

Top Processes by Memory: ⓘ

    1.82 GB Google Chrome Helper(8)

    713 MB kernel_task

    549 MB com.apple.WebKit.WebContent

    385 MB Safari

    328 MB mdworker(12)

Virtual Memory Information: ⓘ

    1.33 GB Free RAM

    6.67 GB Used RAM (2.37 GB Cached)

    0 B Swap Used

Diagnostics Information: ⓘ

    May 26, 2016, 07:07:10 AM    Self test - passed

    May 25, 2016, 05:39:37 PM    /Library/Logs/DiagnosticReports/Microsoft Excel_2016-05-25-173937_[redacted].cpu_resource.diag [Details]

        /Applications/Microsoft Excel.app/Contents/MacOS/Microsoft Excel

    May 25, 2016, 05:09:47 AM    /Library/Logs/DiagnosticReports/Microsoft Excel_2016-05-25-050947_[redacted].cpu_resource.diag [Details]

    May 24, 2016, 07:42:44 AM    /Library/Logs/DiagnosticReports/Google Chrome_2016-05-24-074244_[redacted].hang

        /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

Open system preferences > open the pad lock by entering user name and password > click to schedule > uncheck the box shut down ... everyday ....time .click on ok.

Thanks appreciate and apologies if dense here but after I click system preferences and all the icons come up which section do I need?

Your computer must be awake at the time that it's scheduled to shut down, and remain awake for at least 10 minutes past the scheduled time, in order for it to shut down on its own. If your computer is sleeping at this time it will continue sleeping instead of shutting down. If you've set your computer to go to sleep after less than 15 minutes of inactivity, the computer may go back to sleep before it shuts down.

If you'd like your computer to shut down at a specified time (even if it is sleeping) and you don't need your computer to automatically start up later, you can schedule it to automatically start up 5 minutes before you've scheduled it to shut down.

energy and savers

I thought it may be there but there wasn't a shut down everyday option there are

put hard disks to sleep when possible (was ticked now unticked)

wake for network access (was ticked now unticked)

start up automatically after a power failure (was unticked left like that) 

Computer sleep and display sleep both set at 10 mins

I work from home so on it from 8am till 7pm solid most days

The correct settings are in screen shots please follow them it might help you .

Bad news, it was not the heat from the lamp, my Mac has started to shut down again, i now think it maybe the Seagrave external hard drive, any one else with a problem with this ?

cheers

Having  suffered with this  problem  for  some time, I noticed  that  after  shutting  down and restarting, the  problem  did  not  re-arise  on that day. So now I start up each morning and  then Restart.  The computer stays  on all day and i no longer have the shutting  down problem.  Hope this  is  helpful

I'm a little late to the party here, but my early 2009 iMac has been shutting down for no reason since March, 2016, sometimes multiple times per day - and for those of you suggesting the security settings (done that), by shut down, I mean it just suddenly goes dead - it doesn't gracefully power down. One second I'm working, a split second later I'm looking at a black screen, quiet, no-one-is-home, dead machine.

I have been researching this since then and I have tried ALL of the suggested fixes short of replacing the power supply (there are several with this problem who did, and the problem still occurs) or the logic board (others have done this as well, and it still dies - that's the one that makes this problem so frustrating - that should be the fix for any problem).

You, however, are the first to suggest the external Seagate drive. I have noticed, over the months, that mine dies mostly when file transfer is involved - accessing cloud drives (Dropbox and OneDrive in particular), saving email attachments, or transferring files to and from my Seagate USB drive (this also functions as my Time Capsule drive). It dies on other occasions too, usually when I'm using Safari. It does not die if I am just using local apps or files - there must be an external file or session involved.

I think that I will try to live without the drive for a period of time. I will keep you posted.