(capt) PC powers down unexpectedly - not a heat issue...

This has me stumped.

Desktop PC single Processor AMD Phenom, clean and no dust, air cooled, with 8GB Ram DDR2 and Win7.

This switches off randomly, just as if it has a heat issue. All heat sensors are connected and hardware probes show that there is no unusual rise in temperature at the time of shut off. Sometimes shut off happens at boot, sometime after 10 minutes idle time, sometimes after 1 hour of constant use.

This has been scanned for Virus and Rootkits and is clean.

Symptoms are the same every time, no blue screen, no freeze, no warning of any kind. Just power off. The only difference here can be that 4 out of 10 times you cannot power back on with the switch, you have to switch power supply off and on again.

The PC runs forever in BIOS mode, e.g. booting into BIOS only. It also seems to 'behave' in Safe Mode. But it does not in Windows.

I have completely reinstalled Windows after full HDD format and the problem still persists. So it is not a rogue driver that has crept in or some 3rd party software.

As I said, the symptoms are like overheating but it is not, it does not appear to be a driver issue, so it must be hardware and standard windows function combined, but I don't know where to start diagnosing this.

Anyone any ideas what to do next?

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Let's use the correct terms. Is it a shutdown, a bluescreen followed by a reboot or does it just "blackout", that is behave as if you have pulled the power cord?
Try another PSU, maybe the one you have has defective electrolytic capacitors or just can't output enough power. Also the mainboard could have defective electrolytic caps, so check it visually for signs of them cracking, leaking or bulging. Also try changing the CMOS battery.

It is still possible that the CPU overheats, remove the heatsink, very thoroughly clean both the CPU's and it's surface from any old thermal transfer paste or pads, then apply a very small drop of fresh thermal transfer paste and firmly and properly reattach the heatsink. Thermal shutdowns often happen very fast and don't get recorded. Besides that the thermal sensor might not output correct readings.
captainAuthor Commented:
>>Correct terms

Not sure what you mean, but as I said:
Symptoms are the same every time, no blue screen, no freeze, no warning of any kind. Just power off.

I will check the PSU Monday, will need to find one first :)

I already clean and reseated heatsink, new transfer paste and checked for any discolouration on the CPU. The caps on the mainboard looked pretty new and undisturbed but I will check these again when swapping PSUs.
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Sorry, I tried to read carefully (or so I thought)... :(
Ok, if it's a poweroff, normally the power supply is the cause.
captainAuthor Commented:
No worries.

So I suppose the best course of action is to get a suitable power supply and start from there.

btw. I now had the PC for 6 hours on in safe mode and no shutdown.
can you post the model of pc, or motherboard, along with a couple of specs?  ram, disk setup and size, and connected devices?
you can find most info if you navigate to : start>allprograms>Acessories>system tools>system information
look in hardware for details

any of these can be the cause - so my suggestion is to test with a minimum setup, as described here :
http://www.experts-exchange.com/Hardware/Components/Motherboards/A_1945.html                  (Short-overview-of-how-to-troubleshoot-bad-hardware-when-a-pc-does-not-post)

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Rob GMicrosoft Systems EngineerCommented:
I agree with rindi, sounds like a bad power supply..
Or you have a power strip, surge protector that is failing..
What else do you have plugged into the strip?


What happens if you plug the system directly into the wall.. with the monitor, and nothing else?
captainAuthor Commented:
None of the other items that hang on the same strip go off.

I am  now waiting for a new powersupply, I will isolate that when I receive it and plug straight into the wall.
AaronSystems Administrator & DSTCommented:
I believe this to be the power supply as well. It should be noted that computers use a more delicate flow of electricity usually handled by the power supply but if the wall outlet is providing to erratic flow of electric the power supply wont be able to handle it or overtime can fail. It might be worth it to get a nicer surge protector or a cheap battery backup. If the problem persists after getting a new power supply you should try the battery backup so the flow is uninturupted. Also be sure to get a power supply that can handle the PC needs especially if you have a powerful GPU and CPU as well as ddr2 ram (which is about twice the voltage of ddr3) and some MoBos take a lot too. I think you made the right choice with getting a new power supply it's always good to have an extra if that turns out to not be the problem.
captainAuthor Commented:
Thanks, I should have it by Friday latest :)
another PS is a good test; but in the mean time, you can troubleshoot following the article i posted above
captainAuthor Commented:
Hi nobus

oops sorry in the flurry of notifs I did not see your post.

Hardware Info
AMD Phenom(tm) 9950 Quad-Core Processor, 2600 Mhz, 4 Core(s), 4 Logical Processor(s)

BIOS Version/Date      Phoenix Technologies, LTD ASUS CROSSHAIR II FORMULA ACPI BIOS Revision 2607, 11/06/2010

NVIDIA GeForce 8800 GTX

Marvell Yukon 88E8056 PCI-E Gigabit Ethernet Controller

GPU & LAN both on IRQ 16      

DDR2 only 4Gb Crucial Memory installed...not 8

WD 500Gb x2 in NVIDIA onboard RAID 0+1

Something I noticed just now typing this is that the mouse hangs every few minutes, not sure if dodgy cable or something else, may swap that too..

AaronSystems Administrator & DSTCommented:
Looking at that I would suggest at least a 600 watt power supply though personally I would go with a 650 or 700... Assuming you have a few fans and might want to add more in the future. I know that recomended might not be that high but I always like a buffer. Other experts insist that 500 watts is the most you will ever need but I have never had a power supply issue in my custom builds and I believe that using 650+ watts is a part of that reason.
before buying a PS - calculate how much power you need here :

often you need a lot less than you think - and allow a margin of 50 W

there is a bios upgrade -2702  http://www.asus.com/Motherboards/CROSSHAIR_II_FORMULA/HelpDesk_Download/

you can also install the latest drivers from that page
captainAuthor Commented:
Thanks, calculations show:
Recommended PSU Wattage: 590w
Minimum PSU Wattage: 540w
AaronSystems Administrator & DSTCommented:
Yeah so 650 would be just about perfect it's like a magic number ha ha
you included fans, usb devices etc also?
then yes a 650 W is a good choice
unless you foresee other devices coming ?
AaronSystems Administrator & DSTCommented:
If you want to do ATI Crossfire or SLI 2 cards (assuming you have the mobo slots) make sure that you get a certified ready PSU for crossfire/sli (SLI in this case). Generally you would want a 750 watt+ and make sure it has two 6 or 8 port connectors if needed for the GPUs.
captainAuthor Commented:
you included fans, usb devices etc also?

Yes, I also included USB Scanner. :) To be honest, the costs for the extra Watts are not excessive, so  I may as well opt for 750W.

The funny thing is that they vary from $25 to $100. What level of expense is sensible? Cheap may not last that long or is not an SLI compliant PSU but is $100 necessary?
AaronSystems Administrator & DSTCommented:
I would say 40-60$ gets you about what you need. I would stay away from any under 40 and over 80 it better be 700+ watts and gold cert.

Here is one:

And it is crossfire/sli capable so if you want to expand later.
captainAuthor Commented:
So I have been sitting here for the best part of a week and the PC is stable as it can be. The only issue is that it is stable with the old PSU...

I am baffled.

Naturally I am loathed to swap things for swapping sake. So I will continue monitoring this and swap when needed.

I think I can close this out as the consensus is PSU.
it is the first device that comes to mind; but it can be other devices as well
captainAuthor Commented:
almost 2 weeks on, and I still have not swapped PSUs as no fault has occurred.

I will see what happens over the weekend under heavy use and either close or report back.
are all devices connected?  if not, do so
as a test, you can update all drivers allso
captainAuthor Commented:
Lots of use over Christmas, no problems at all. I kept the power supply for spares but have decided to not mess with the setup unless the problem emerges again.

Thanks for all the help. Will split for new year.
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