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I finally decided to take the plunge and build my own PC. All in all the actual construction went pretty well and after a couple of hours tinkering I managed to boot it up for the first time which is where things started to go wrong. After installing the operating system and a few basic programs (anti-virus etc.) my PC has started to randomly turn off and reboot, usually when I'm streaming or watching video, but not always.

Steps I have taken so far include:

  • Update all motherboard and graphics card drivers from manufacturer websites
  • monitor temperature of CPU and hard drive (both are well within the limits)
  • Uninstall and reinstall windows and make sure it's fully updated
  • Open the PC and check all the connections
  • Replaced the mains power lead

And this is what my PC looks like:

  • Intel core i5 760 2.8 Ghz
  • GeForce GTX 460
  • Corsair Dominator 4GB DDR3
  • Gigabyte GA-H55m-S2H motherboard
  • Samsung Ecogreen F2 1TB SATA-II HD
  • Sythe Yasya CPU cooler
  • OCZ StealthXStream 2 600w PSU
  • Windows 7 Home Premium 64-Bit

Any help would be much appreciated.

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Does it actually do a soft power down or does it just cut power and then reboot? – BloodPhilia Sep 24 '10 at 14:17
Double check your temperature monitoring. This is often a heat issue and re-seating your heatsync "can" be a simple fix. – Chase Florell Sep 24 '10 at 14:22
A friend suffered from a seemingly random reboot for two years! until we checked and found a bad memory module. The memory check program rebooted at the same position on each attempt. – W_Whalley Sep 24 '10 at 14:57

The part list sounds pretty mainstream.

It's a wild guess but did you put a good heat-sink compound on your CPU? It sounds like a heat issue and if you're not overclocking then the thing to look at would be cooling of CPU. Even a great CPU cooler is useless without a good heat-sink compound. Also it must be applied properly, which isn't as easy as it sounds.

If you're certain the CPU isn't the problem then you might try watching those video streams with a different OS, say one from a live-CD so you don't need to commit to any changes. If they also fail under a second OS then it's pointing at the CPU again. If they don't, you might consider a backup and re-install since the system you have should work really well.

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If the other soltuions don't work, I would check your memory as well... especially that it's seated properly, and clean. Test the memory using Memtest86+. Here is a simple guide on how to use memtest and clean the memory. You also have to make sure that the memory is seated on the same channels as well. This is an article on what the separate channels are.

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One way to diagnose this is to remove as much hardware as possible (all but one RAM module if you have more than one, all but one disk drive (either CD/DVD or hard disk, drop down to the motherboard video chipset if any, etc.) If this configuration is stable, add one more device (say the video card) and see if it's still stable.

You can boot a liveCD with the hard disk disconnected to see if that device is a problem. You can even stream and watch video off Ubuntu or Knoppix.

If you have or can borrow spare parts, you can try swapping in, for instance, a different RAM module and a different video card (one at a time!) to see if those devices are the problem.

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Look at the Window's "Event Viewer" and see if it logs any errors or malfunctions to be followed up with.

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If you haven't monitored the temperature of the video card, GPU-Z will do that for you.

SpeedFan is also very good at displaying all temperature sensors in the computer.

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