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For the past 2-3 days my computer has been automatically turning off. I can think of three reasons:

  1. I have very cheap grade power supply and it may be that it is not able to supply enough power, so if power requirements increase the computer turns off.

  2. My hard disk is faulty because the following has happened to me twice: when I restart my computer it says "disk not found". Then I turn it off, wait 5 minutes, start again and it's working again.

  3. Maybe my CPU is overheating and cuts off the hard disk.

I don't know what is the problem. Is there any way to find it out?

A few additional notes:

  1. My computer always stays on and I use it for downloading things using IDM

  2. When I turn off my computer, I can still hear the CPU fan running. The hard disk turns off and my mouse light also turns off.

  3. There is one other thing that happens after this. If I restart my computer, a message pops up from that IDM software. If I click "Install", it installs some files to my Windows directory in 2-3 seconds and after that an IDM icon appears. This usually doesn't happen after a normal restart. Maybe the IDM software consumes too much power and it causes the system to restart?

My computer is a desktop with a Pentium 4, 2 GB of RAM, and only a DVD-burner and hard drive attached.

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What kind of computer is this? What CPU? – David Schwartz Jan 17 '12 at 9:58
Desktop Computer P4 2Gb RAM , Only DVD RW and HD Attached – user1146320 Jan 17 '12 at 9:59
If your computer is turned off, its not possible for the cpu fan to still be running, "turning" off disrupts the power to the motherboard. – Ramhound Jan 17 '12 at 12:14
I think only harddisk gets turned off and everything else which is connected to USB. Even cd drive also works fine at that time – user1146320 Jan 17 '12 at 14:03

How can I see the last temperatures (CPU, HDD, GPU) before my unattended PC shuts itself down?

Use HWmonitor together with AutoScreenshot to save the last state. This combination will take a screenshot every minute of your system temperatures until your PC freezes or shuts down automatically. It will overwrite the last screenshot so only one file will be hold. (Can be configured)

It has some additional benefits. You also see the time when your PC shuts down and you see possible pop-up messages from any software.

On the next morning, just power your PC on again and look at the screenshot. Voilá.

HWMonitor is a hardware monitoring program that reads PC systems main health sensors : voltages, temperatures, fans speed.

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AutoScreenShot is like a camera for your computer's screen. Can record everything displayed. Very usefull if you to know what happen on your computer when you'r outside

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Remember that you have to disable Windows AutoLock and other power saving options. Only the monitor can be turned off.

Reduce the most recently pictures counter to an amount that fits your needs and set a higher delay between two shots.

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The best way I found for logging temperatures with free software is using Speedfan. You must enable logging in the settings. Here is a little guide on how to set it to log the various sensors. You are interested in the CPU and MB temperatures, as well as fan speeds.

Speedfan will save the log as a csv file in the executable folder. You can open the file with any text editor or you can import it in Microsoft Excel or OpenOffice Calc to see the data as a table.

You should use a stress test program such as IntelBurnTest. This will ensure that the CPU is running at its maximum power.

To diagnose hard disk problems, you could check the Windows Event Viewer for error messages about HD and controllers, or you could make some tests by copying large files or running a chkdsk /R.

To diagnose PSU problems, I'm afraid the only possibility is to replace it with another PSU and test the system.

Consider that your problem might also be caused by a faulty/damaged motherboard. A damaged disk controller might cause the "disk not found" thing.

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I would recommened a tool called Speccy from Piriform.

It's a system information tool for Windows and will give you all sorts of data including CPU temperature.

If your CPU is overheating then there's a couple of things you can check. First, ensure you have proper air flow inside the case. Give it a good clean and tie up any cables that are hanging loose. Secondly, clean the CPU. Get some CPU cleaner, remove the old thermal paste and re-apply some fresh thermal paste and reseat the CPU.

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Is there any way that if computer got turned off then i can see what was the temmpertaure when computer turned off – user1146320 Jan 17 '12 at 10:08
I'm not sure there is anything that will report back and specifically say "Computer turned off at xx:xx due to CPU overheating" but you could check the Event Viewer and look for 'Kernel-Processor-Power' events in the Source column under the System log. That will give you some indication as to when it powered off. There might be a detailed message there though, take a look and paste it back here. – Moif Murphy Jan 17 '12 at 10:15
i get this error 41 The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly. – user1146320 Jan 17 '12 at 10:36
So there you go. You have a date and a time and some kind of reason but I'd give things a clean and monitor it for a while. – Moif Murphy Jan 17 '12 at 10:43
It happened again just now. Hardisk was off. I presses DVD drive and it came out. It means motherboard is ON. does it mean that hard disk can be faulty – user1146320 Jan 17 '12 at 13:39

This PC World article recommends a free program called Core Temp. The author concludes that CoreTemp helped him save his computer and avoid an unnecessary and costly upgrade to a whole new system.

From the Core Temp website:

Core Temp is a compact, no fuss, small footprint, yet powerful program to monitor processor temperature and other vital information.

What makes Core Temp unique is the way it works. It is capable of displaying a temperature of each individual core of every processor in your system!
You can see temperature fluctuations in real time with varying workloads. Core Temp is also motherboard agnostic.

Core Temp screenshot

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