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My Windows 7 computer started shutting down seemingly randomly recently. Basically, within a 10-120 seconds from hitting the power button, the computer just powers off as if I unplugged it. No BSOD, no error message, nothing.

I put the tower on it's side to check the connections of all the cables inside. WHen I hit the power, it booted! Great, I thought. I stood it up and it shut down again. I put it on its side and it ran flawlessly again.

What is going on? Loose connection somewhere? I really don't want to keep it on its side forever.

Update:

  • The tower is on its side.
  • The side cover (which is now oriented on the top) is off.
  • The motherboard is now parallel to the ground.
  • Booting to a Windows 7 install disk still failed.

I'll check the HSF next...

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2  
Check your processor heatsink is firmly attached. –  Mike Fitzpatrick Aug 13 '11 at 2:02

3 Answers 3

up vote 6 down vote accepted

I would suspect the heatsink/fan (HSF) is not firmly attached to the CPU socket, causing the CPU to overheat and shutdown. When the tower is upright, the motherboard is vertical and gravity will pull the HSF away from the CPU. When you put the tower on its side, the motherboard is horizontal and the HSF will be sitting atop the CPU, providing enough pressure to keep the CPU running longer.

You can confirm if it's a temperature issue by watching the CPU temperature between power on and power off. Your BIOS should have a temperature monitor. Power it up, boot into the BIOS, go to the monitor page, and watch the CPU temperature prior to the power off. There are also plenty of temperature monitoring programs for windows, such as Speedfan, but you may not have time boot into Windows and launch the program before it powers off.

If the HSF feels wobbly, check the CPU socket clip that holds the HSF in place, or the screws if your HSF is one that attaches directly to the motherboard. You may need to remove the HSF, clean off the old thermal paste, and reattach it after applying a thin layer of thermal paste.

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Absolutely agree that this is the first place to look, and the best way to test for it. If it isn't that though, one thing to check that hasn't been mentioned is the PSU. –  ZoFreX Aug 13 '11 at 4:32
    
three of the four screws were loose. i took it off and added thermal paste but i guess the oils from my skin made it worse. took off the cpu and the fan, cleaned it with alcohol, re-pasted it and reseated it all. everything seems to be working fine. thanks for the advice! –  Jeff Aug 14 '11 at 0:00
    
what is a normal operating range for the temperature of non-overclocked cpu? according to SpeedFan, everything is around 50-60* C but "Temp3" is at 127*. –  Jeff Aug 14 '11 at 0:22
1  
50-60C is fine. The system will automatically shut off, as you experienced, somewhere around 90C or so. 127C (all one-bits set in an 8 bit integer) indicates there is nothing connected to that particular temperature sensor. Nothing to worry about. Looks like everything is back to normal! –  cantfork Aug 14 '11 at 16:48
    
thanks so much gordoco! i wish i could upvote you more than once. –  Jeff Aug 15 '11 at 13:34

Go through everything in the case and re-seat it. Take note of anything that is even remotely loose.

Also try unplugging your HDD and see if it at least boots to the point where it complains about not having a HDD, if it does it could be causing the issue and you'll need a new one.

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Do you smell anything burning behind your power supply? I had to replace mine to fix unexplained reboots that hit me about 2 minutes into a cold bootup for my old Dell dimension. And speaking of burning, check that your capacitors aren't leaking or bulging. A few years ago this used to be very common.

Computers that randomly power off usually have an un-fixable motherboard issue, or a newly manifested heating problem. You aren't going into detail about your headline of "runs only on its side." It could be that you are taking the "lid" off and only see it run stably the moment that air circulates freely and keeps the PC much colder than when you stand it up and set the airflow back to normal conditions.

You might need to get a whole new PC, though. The final test of truth is to see if active use of a different operating system still suffers from the same powerdowns (downloaded Ubuntu LiveCD or LiveUSB). If it doesn't, it could be some updated driver that will require you reinstall your whole Windows rig.

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The tower is on its side. The side cover (which is now oriented on the top) is off. The motherboard is now parallel to the ground. I ran the computer like this with the side cover off and then with it on and it hasn't shut down. That leads me to think that it isnt a circulation issue. –  Jeff Aug 13 '11 at 14:16
    
I'm glad to hear the problem seems to be resolved. PC hardware has many points of failure. –  Vlueboy Aug 14 '11 at 3:08

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