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My computer reboots, seemingly completely at random, about once every week to two weeks but has occasionally gone months. It just goes from running fine to the POST with no error messages or anything and doesn't seem to be due to heat or usage as it's happened a couple of times when the computer has booted just a few moments ago and is idling. It's been happening for as long as I've had this computer, almost two years. It's happened in both Vista and Windows7.

I strongly suspect it's a hardware problem. But due to the rareish and random nature of the crashes my normal strategy of just removing hardware until the problem stops isn't really practical. My guess would be Power Supply, Ram, or Motherboard. But I just don't know how to test an issue this random and want to figure out how to confirm which it is before I go replacing things. So is there some software or hardware that can be used to test these sorts of errors? I did run memtest86 for about 8 hours without finding any issues. And the power supply is more than capable of running my system.

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It certainly seems like a hardware issue.

The first course of action would be to test your ram. Memtest86+ is a widely used diagnostics tool for RAM. I suggest you leave it running overnight or longer and see if it reports any errors.

If your RAM seems to be alright, you can try running a CPU burn-in tester to see if your processor is alright, if it doesn't produce strange faults.

If that doesn't produce any errors you could try to replace your BIOS battery. I have seen examples in which an empty BIOS battery somehow made a system instable. It's also a cheap solution.

My last guess would be the PSU. Replace it with any decent and recent model and test RAM and CPU again.

A note: if you test RAM, leave as much hardware out as possible.

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I won't repeat the guides others have written - you should start by disabling automatic restarts and doing a memory test (forget this though as you already have).

AFter this, Take a look at Bluescreenview, this utility will allow you to see any bluescreens that have appeared in the past and hopefully allow you to track down the fault.

As for the fault itself, the number one cause in older machines is Blown Capacitors, I have attached my little guide:

Blown capacitors -

Blown capacitors can be the cause of many "random" problems which appear to be completly unrelated, very annoying and hard to diagnose.

alt text

The top should be almost flat (with slight indents out embossed sections depending on specification... look at the middle one) but you do not want to see any big bumps such as the first one or any leakage as the last one.

Hope this helps.

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Turn off automatic restart (the instructions are similar for Vista and 7) and see if the computer is BSOD'ing and get the stop codes. You can also look into the event log under "System" and check for critical errors.

Otherwise, "acquire" a copy of PC Doctor and run some extended diagnostics.

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Just to add to the good advice of others above I will add my 2 cents. In my experience the first candidates to check for random reboots and hardware problems are your power supply and cpu cooler. If you have multiple drives & devices and a power supply that is getting on a bit then that would be my first guess for causing the reboot. The other alternative culprit can be heat. If the system is overheating then it may be restarting itself - heat should be easy enough to monitor.

Overall - sounds like a good excuse to update to me - buy a new one!

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1  
+1 for heat, I just had a similar issue, those stupid plastic heat sink push pin connectors are terrible. – Mark Robinson Apr 9 '10 at 12:00

I don't know about windows-7 and Vista, but on XP you can look at the event viewer to give you some clues. On XP you right click on "My Computer" and select "Manage", then click "Event Viewer", then double click "system". This will show all sorts of events that were happening on your PC just before the crash, including ones labelled "Error".

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The problem is that this can be tied to almost any piece of old hardware going into a slightly odd failure state. The hardware could be 99% perfect but it's that 1% that gets you.

I've had a similar problem with my machine of 5 years now and only managed to kill the random reboots about a year ago. I had two particular modes of failure. First one is that windows would appear to hang and then the machine would reboot and the main hard drive would not appear on the BIOS POST screen so that got replaced and got rid of that problem. The second issue was exactly what you are describing, a completely random reboot out of nowhere which I only killed on a hunch that the oldest piece of hardware in my machine was an 8 year old CD-writer that had migrated from an old machine. After removing these two parts my machine has behaved quite well.

Don't just be looking at the mobo, suspect the hard drives and other peripherals too, HDDs can make your computer "pause" or appear to temporarily go dead on a bad block and then windows may reboot as a result. In my case the drive failed to appear after reboot but yours could be able to recover during the reboot. If this is the case then an error log would show nothing as it cannot be written to as the hard drive is missing.

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this may seam strange but it is the problem more times than not... check your fans... the bios will typically shut down or reboot if it senses a fan failure, typically a failure is nothing more than the fan not spinning at a minimum fan speed. for about 5-10 dollars the fan can be replaced, or if you have compressed air, clean it up in there. another option is to check bios and set the minimum speed lower or disable the protective mode all together (not recommended). often times a PWM fan may actually shut down for a bit if temperatures are o.k. when it shuts down it may cause this issue.. the settings in the bios can actually contradict each other and cause these issues. but more than liley you have a old fan that is slowing down, enough that the bios sees it as a potential danger causing the reboot.

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Curious why the downvote? I'm no PC hardware professional, but seems legit and well explained. – Ogre Psalm33 May 24 '14 at 17:16

In my 17+ years of PC tech experience I've noticed that, when I'm working on a new build, or my latest PC that isn't completely upgraded yet, I always seem to get random restarts when I'm still using the onboard graphics card, and it doesn't matter how good the onboard video card is because they all have to share system RAM since they never have enough. The use of the onboard graphics adapter on your new motherboard will always cause problems because you're mixing graphics and audio data, with Windows and system data, which always causes software conflicts and stability problems within RAM. The fix for this is simple: install a nice PCIe video card with at least 2 GB of VRAM – that way you're no longer mixing video data within your RAM.

If and when you have to run the onboard video card, the best thing to do until you can upgrade your graphics card is to turn off auto restart after a BSOD or serious system failure. Since these types of restarts happen so quickly, and even when you're away from the machine, you don't get to see any error messages to help you locate the problem area or device. Intermittent restarts are never good for Windows and are usually worse for the OS than the problem that caused them in the first place, especially if you're away from the PC when it happens.

To turn this behavior off:

  1. Open Windows Explorer (or just go to the desktop), right click on "Computer" and select "Properties".  On the left, click "Advanced System Settings".  (This will invoke a UAC dialog.)
  2. Find the Startup and Recovery section at the bottom of the window and click on "Settings".
  3. In the Startup and Recovery window, locate and uncheck the check box next to "Automatically Restart".
  4. Click "OK" until you're out of the window. No restart is needed.

Now, when a problem occurs and you get a BSOD or any other major errors that would normally restart the system occur, Windows 7 will not reboot, but you will have to reboot manually whenever an error occurs so Windows can attempt to correct them.

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Hi, welcome to Super User, and thanks for your answer. In the future, please abstain from including irrelevant links, as they may be flagged as spam. – Ben N Feb 16 at 18:06

Sharing my experience about spontaneous reboot. For me the culprit was PSU. If you have got the same symptoms as mine then it's definitely PSU.

Symptoms: Random restarts, whether in BIOS or Windows. First restart has long interval then restarts at short intervals. Occasional RED colour Bios screen CPU fan revving on start or sudden heating up even when idle or in BIOS screen.

Do check for blown capacitor on Motherboard.

I did the paper pin test and multimeter reading of voltages at various pins. All was fine but PSU was failing under load conditions.

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