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My computer keeps shutting down instantly when I'm in Windows – as if you pulled the power cord. There's no bluescreen or anything like that. Then, it starts up again. This happens at random after around 5-60 minutes of uptime.

If I enter BIOS setup, I can leave the computer running for days without this problem. That shows that my hardware should still be ok.

Where would I start troubleshooting? The event log looks good, and since there is no bluescreen, there are no other error messages to go after. It's like the power is cut off instantly, and then the computer just reboots itself.

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have you turned off automatic restart? like, xp has an automatic restart option you can turn off, maybe if you turn it off you'll see a blue screen. Maybe there are things in your event log. In XP at least, look for red xs, and then if I recall, look for exclamation marks. I think I might've had a CD drive related thing give an exclamation mark in an event log(application or system i'm not sure), and I found that might've happened at the same time as a restart and I addressed that. maybe stopping a service related to it or something. a strange problem but anyhow, look more in the event log. –  barlop Mar 10 '12 at 22:22
    
I have heard of restarts not appearing in event log though, a power fault might do it like a bad power supply..other than that, perhaps, as mentioned, perhaps ram or cpu. –  barlop Mar 10 '12 at 22:23
    
What type of video card are you running? It might be that it is fried or just to old to.run your requirements. –  onxx Mar 10 '12 at 23:11
    
Your conclusion is incorrect - it is likely to be a hardware problem. Many components run in a quite different way when you are in the BIOS (16-bit mode) than they do when you are in a 32-bit or 64-bit operating system. We had a very similar problem with some of our machines a few years back which was resolved by reseating the CPU. –  Harry Johnston Mar 16 '12 at 0:16
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1 Answer 1

It could be overheating. Install SpeedFan from http://www.almico.com/speedfan.php and see if it reboots when the CPU hits a certain temperature.

If it's not that, try running Memtest86 from http://www.memtest.org/ to see if there are any memory faults.

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