Why is my imac shutting down by itself?

Count my machine too... So frustrated.. Can't rely on Mac these days.

Good news today my Mac has not closed down, thinking it maybe heat i have turned off a desk light that i have right next to it, so far so good, will keep you posted

I am wondering if you perhaps stumbled onto the solution, or at least a part of the solution. My thoughts are that is it possible that the infr-red pickup used for the remote control may be getting :jumbled" info that it sometimes interpets as a shut down command or something similar? If so, turning off infra-red may give some people the cure.

Here, from the Help files, is the way to turn the infra-red receiver on (or off).

Turn on IR reception

Choose Apple menu > System Preferences, click Security & Privacy, then click General.

Open the General pane for me

Click the lock icon to unlock it, then enter an administrator name and password.

Click Advanced.

In the window that appears, deselect “Disable remote control infrared receiver.”

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 .