IMac shuts down periodically

Imac shuts down occasionally when there is no power outage. Was trying to figure out why this happens.
Any suggestions? Are there specific logs that might help?
Thanks for the help

Check the Energy Saver preference pane for scheduled shutdowns. If there are none, see below.
These instructions must be carried out as an administrator. If you have only one user account, you are the administrator.
This procedure is a diagnostic test. It makes no changes to your data.
Please triple-click anywhere in the line below on this page to select it:
syslog -k Sender kernel -k Message CSeq 'n Cause: -' | tail | awk '/:/{$4=""; print}' | pbcopy
Copy the selected text to the Clipboard by pressing the key combination command-C.
Launch the built-in Terminal application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Terminal in the icon grid.
Paste into the Terminal window by pressing the key combination command-V. I've tested these instructions only with the Safari web browser. If you use another browser, you may have to press the return key after pasting.
Wait for a new line ending in a dollar sign ($) to appear below what you entered.
The output of the command will be automatically copied to the Clipboard. If the command produced no output, the Clipboard will be empty. Paste into a reply to this message.
The Terminal window doesn't show the output. Please don't copy anything from there.

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Yes I do live near a ghost town (kinda) - Virginia City, NV. And I did tell any unwanted visitors to leave.
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Hello there, TheCapGuy.
The following Knowledge Base article is a great resource for steps in troubleshooting spontaneous restarts:
OS X: When your computer spontaneously restarts or displays "Your computer restarted because of a problem."
http://support.apple.com/kb/TS4636
Thanks for reaching out to Apple Support Communities.
Cheers,
Pedro.

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Before Resetting the SMC
Try each of the following steps in this order before you reset the SMC. Test the issue after completing each troubleshooting step to determine if the issue still occurs.
Press Command + Option + Escape to force quit any application that is not responding.
Put your Mac to sleep by choosing the Apple () menu from the upper-left menu bar and then choosing Sleep. Wake the computer after it has gone to sleep.
Restart your Mac by choosing the Apple () menu from the upper-left menu bar and then choosing Restart.
Shut down your Mac by choosing the Apple () menu from the upper-left menu bar and then choosing Shut Down.
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Resetting the SMC for Mac Pro, Intel-based iMac, Intel-based Mac mini, or Intel-based Xserve
Shut down the computer.
Unplug the computer's power cord.
Wait fifteen seconds.
Attach the computer's power cord.
Wait five seconds, then press the power button to turn on the computer.
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http://support.apple.com/kb/HT3964
Best Regards,
Jeremy

Imac shut down

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First check System Preferences - Energy Saver - Schedule and see if someone accidentally scheduled shut offs. If that is unchecked then you probably have a power issue, get your power and plugs checked where the machine is located, if the machine is on a UPS and the power issue is cause by your wiring or power company then the UPS can at least make it easier on teh system so it can do orderly shutdowns.
If the power checks out OK then run Apple Hardware Test in extended mode at least 3x, if errors appear you have verified a hardware problem and need to take the machine in for repair. Don't ask what the codes mean, Apple does not publish that information. AHT is not the most reliable test but it's what you have, if it doesn't report errors that does not rule out a hardware issue, meaning you should still take it in to be checked by your local Apple Store or AASP.

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Your profile does not indicate what version of iMac you are running. Take a look at this to determine if your system falls into one of the categories:
http://www.apple.com/support/exchange_repair/imac.html
Barry

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So my imac shuts down randomly all the time, after it turns itself off, u need to unplug it for ages, then it will restart (way longer than it should to reset smc). Even in target mode,
Even stranger is it logs a console message stating, system must shutdown now, shutting down....
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I've experiencing the same problem.
If there is a power failure (or the power line gets disconect) I have to unplug everything from the back of the computer and wait for hours till I can turn it back on.
Recently it started to turn itself off..... and then I have to wait for several hours till I can get it to work again..... any tips on how to solve this?

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Imac shuts down about 5 seconds after starting.

Aubrey2320 wrote:
iMac, purchased last year
If you are still under warranty and/or have AppleCare, call them. Let them deal w/it.
OOW: Take your Mac to your local Apple Store or an AASP. Diagnostic testing is FREE!
Other OOW options:
How to save money on Mac repairs with your credit card’s extended warranty
Troubleshooting not working.
There is nothing anyone here can do as you did not provide any of the steps you've tried to solve your problem. Need details to avoid the been there done that scenarios.

IMac shuts down periodically

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