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My computer is about 7 years old. Its has an Asus A7N266-VM motherboard and an AMD Athlon XP 2400+ CPU. My problem is that my computer suddenly and randomly switches off on its own. There is no blue screen, no error messages, the pc just goes off as though somebody pulled the plug. The motherboard power indicator LED remains ON. It might happen anytime from within 5-10 mins of starting up, to maybe an hour or two later. Sometimes it works perfectly fine and never turns off. And once it shuts itself off, i can't power it back on. If i press the power button to start the computer, it turns off again in about 2 seconds before even the POST can start. If i pull the plug and try again later or shake up the chassis a but and retry, it might boot up again and run for some random period of time before the same story repeats.

Another (maybe) related problem which i have been facing for a longer time is that my computer cannot be shutdown. After windows(xp) shows "Windows is shutting down..", the system powers off and promptly restarts. So all I can do is pull the plug at the right instant!

Any ideas/suggestions?

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Guys, thanks for all your responses, but has anybody given any thought to the other problem, ie., the system not shutting down when it is supposed to? I was wondering whether these two issues could be related.. –  Felix Sep 20 '10 at 15:21
    
A little tip with the shutdown problem.. while I don't know the cause. I can tell you that instead of pulling the plug, try keeping the power button pushed for a few seconds. And regarding the power Led light, going off when you move the computer, then that could just be a lose connection regarding that little cable connecting to the motherboard. You should open the case and have a look. And regarding checking the power supply. –  barlop Sep 21 '10 at 0:18
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10 Answers 10

Got another power supply you can swap in for testing? If not debris in the case, could be a power supply failing.

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+1 on faulty power supply. The light on your motherboard could be a false indicator because PSs supply more than one type of current (+-12, +-5 I think) so the fact that some power is flowing doesn't indicate that all is, or even that it is correct. –  Larry Smithmier Sep 20 '10 at 13:40
    
@Brian,Larry: Even my suspicions are now moving towards the power supply. I observed that at times, the motherboard power indicator LED also goes off when I tilt or move the chasis. I do not have a spare power supply to test, will try to get one from somewhere. –  Felix Sep 20 '10 at 16:15
    
@Felix You could try putting that faulty power supply in another computer perhaps one that you don't care about that much, and see if it suffers the same problem. –  barlop Sep 21 '10 at 0:23
    
Another thing you could do is test it with a multi-meter. But that will just pick up a basic problem like voltage fluctuations detectable by multi-meter. (i've heard there are changes in the current undetectable by multi-meter that can still mean a bad power supply. but if a multi-meter shows it then it's worse!) But even if that's the case, it could be the cpu or a power supply problem of a different kind -like power going completely! - unrelated to what you detected. –  barlop Sep 21 '10 at 0:24
    
With a multi-meter You may just find all the current stops and the power supply stops.. (apart from maybe 5VSB or something).. And it won't tell you anything.. If keeping that power supply in there, then you need to find the trigger. Try just sitting in the BIOS and see if anything happens. Some BIOSs show CPU temp too. –  barlop Sep 21 '10 at 0:26
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I think overheating is very likely, if as you say, it shuts down then doesn't turn on straight away(it could be cooling down). I have heard of that as a symptom or possible symptom of a system overheating and may have encountered it myself once or twice. Typical candidate for overheating would be CPU. Run speedfan, and see if you see a Temp go up and up and reach a certain point, then the computers shuts off!! or touch the heatsink and see if it is too hot to touch.. ! (the inside of a computer won't kill you.. it's DC and not high voltage. Though many might turn a computer off before doing so.. it's fine.. i've done it!

You may want to take precautions for static. Some people worry about that.

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If it is a old computer it might have lots of dust and cak inside the case, causing it to overheat. Take the case off and have a look, then give it a clean if need be.

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i already tried cleaning the cabinet thoroughly multiple times –  Felix Sep 20 '10 at 10:53
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@Felix - have you tried monitoring the temperature levels in the case? This would allow you to 100% rule out overheating. Check out this question for suggestions of software to help you do just that. –  DMA57361 Sep 20 '10 at 13:19
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Make sure the internal fan is working. If its unable to dissipate the heat, the processor will overheat causing the computer to shutdown.

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Yes, i kept the case open simply to watch the CPU fan. The CPU fan and the computer seem to turn off almost together. In fact, I can see the fan slow down to a stop a couple of seconds after everything goes blank. Don't know what to make out of all this. –  Felix Sep 20 '10 at 16:08
    
Try replacing the fan. If that doesn't work, it may be an issue with the motherboard... –  Mark Sep 20 '10 at 19:56
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If it's not heat, it may be a bad heat sensor. See if there's any log entries about why the box shuts down.

(I'd still go with replacing the PSU first though.)

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This sort of thing is hard to diagnose. If shaking the case can temporarily fix it, it might be a bad cable, or a cable that isn't solidly plugged in. The simplest, quickest thing to try is to unplug all the cables, clean the connectors with isopropyl alcohol and DRY THOROUGHLY, then plug them back in. Do NOT unplug them all and clean them in a big batch unless you're an expert, because it's too easy to forget how to plug them back in. :)

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I have experience with such a problem. My problem was the CPU overheating. When the CPU reaches a certain degree, the computer powers off immediately. Try checking the fan/cooler and the power supply.

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That motherboard is known to be affected by the 'bad capacitors' issue so it may be that too.

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Bad capacitors might be it for such and old motherboard. You can diagnose it by opening the case and looking at the capacitors, which might be bent from the top. You can see pictures from this wikipedia article.

If you are not electronics expert, I suggest that you buy a new motherboard.

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I agree with this statement, the issue is most likely bad CAPs, you can visually check the board for leaking or bulging capacitors and if you see signs of this you should replace the motherboard. Unexpected shutdowns can cause errors on your drives. –  jtreser Oct 4 '10 at 14:58
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A LOT of cases of faulty RAM are mis-diagnosed as overheating, for instance - check that your RAM strips are clean, free from dust, and properly seated in their slots, and disable the "Fast Boot" option in your BIOS to see if any problems are reported at boot-up.

You can also run a Memory tester (I use http://www.memtest.org/).

On several occasions I have experienced, random reboots have been caused by the way XP handles serious system crashes - rebooting rather than displaying the BSOD (check Control Panel / System / Advanced / Startup And Recovery for the checkbox to disable this behaviour).

If you now experience BSOD messages rather than reboots, you now at least have more information to post regarding the problem :).

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