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PC still turning itself off

geoff_austin asked
Last Modified: 2012-05-07
Dear Experts,

Please see my previous question for the history.

I have a replacement processor in the PC now and I have reset the CMOS, formatted the hard drive and reinstalled windows.  However the PC keeps on turning itself off without warning.

The CPU clearly was dead, because previously the PC wasn't booting at all.  With the alternative CPU the machine is 'working' however it will just randomly turn itself off when you're in the middle of something.

After it has turned itself off the light on the front blinks on and off every second and it won't let you start the PC up again until you have removed the power cable for long enough to make the light stop blinking (about 5 seconds).

It must be a hardware fault as it's a brand new installation of windows.  The CPU was working fine for my friend, so I guess it can only be the mobo / memory / HDD.

Has anyone got any suggestions before I take it down to the car park and drive my car over it repeatedly?

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Most Valuable Expert 2015

That's overheating. Have you properly applied just a very small amount of thermal transfer paste to the surface of the CPU, and cleaned off all old residue from the heatsink, then firmly reattached it to the CPU? Also have you checked the Fan is running smoothly?
Sounds to me like the power supply isn't giving the motherboard enough juice to work with and it is shutting itself down to protect itself.
Double check...make sure that all the fans are working properly...I going to say as well...overheating. Do you get or hear any beeping...

It's one of two things:

1. Power Supply
2. Overheating

1. Try disconnecting non critical devices to power supply (CD-ROM, floppy, etc.) Just connect hard drive and try to boot. Make sure the wattage for your PS is enough to cover your MoBo and devices.

2. Make sure you case is clean and fan's are working properly. You should be able to check the BIOS after a "reset" and see the CPU temp, check against manufacturer specifications.



Thanks for all the replies.

Yes, I used some more thermal paste when I put the new chip in.

I have checked that all the fans are working properly and I have blown out the worst of the dust to ensure good air flow.  However when looking at the BIOS the "system fan" speed is not budging from 0 rpm.  I suspect this is misleading because I can't see any fans that aren't running.

According to the BIOS the system temp is currently 36 degrees C and the CPU is 34 degrees C.  The system temp crept up from 31 degrees when it was first booted up.  Is this the kind of temp you'd expect?

If it is overheating then what could be causing it??

<If it is overheating then what could be causing it??>

It could be the case...tower that it's in...that could be causing the overheating...It could just be a not great design...
Most Valuable Expert 2015

"Yes, I used some more thermal paste when I put the new chip in."

You shouldn't add "more" paste, but rather completely clean off all traces of the old paste (or whatever was used, sometimes a pad is used, or some other agent that melts on first use and then hardens, all those are only meant for one-time use). After that only very little paste (a small drop) should be applied. Firmly attaching the heatsink will then evenly distribute the paste to fill any tiny dents or cracks. If too much paste is used, or the old stuff is still there, you get the opposite effect, the old residue or the too-much paste insulates the top of the CPU from the heatsink, effectively preventing it from doing it's job.

Also, the temperature readings are often not accurate. They depend on what type of sensor is used and where it is placed. If it is reading the temp of the heatsink, and that isn't properly attached to the CPU, the heatsink will stay "cold", while the CPU is burning hot.

The CPU's of today have thermal "fuses", if they get too hot, they shut down, and prevent you from immediately turning the system back on. Also usually a LED will start blinking. This is exactly the symptoms you have.
Most Valuable Expert 2013

Not convinced about the overheating - try this utility to monitor what's happening
Very likely it's motherboard though.  Have you checked it over for blown capacitors, burn marks etc?

34/31 degrees C should be too hot but its not chilly. You may have a bad sensor or a poor heatsink. When the computer shuts down can you touch the heatsink to see if its distibuting heat. You could also open the side case and point a fan at it to see if it will stay on for a bit and stay cooler.


Thanks again for all your replies.

Turned on the PC this morning and it switched itself off after barely any time.  The case is open and nothing inside feels particularly hot.  That was at least an hour ago and the light is still blinking.  If it only takes 1 minute to overheat it shouldn't take so long to cool down surely?!

MASQUERAID - Thx for the linky.  Before it shut itself down I did get a chance to install the hw monitor but the only component that was listed was the hard drive.  Not sure if the program needs a reboot before it can list more components??  

I spent ages looking for the model number of the mobo so I think I would have spotted a blown capacitor.  All looks to be OK from what I can see.

Unfortunately I don't have any spare motherboards I can try, or CPU fans.  Looks like I'm going to have to start spending money.... or.... which is looking more and more appealing.... chuck it in the bin and buy a brand new shiny one.
Most Valuable Expert 2015

Have you removed the heat-sink again and cleaned everything very thoroughly, then added the small drop of thermal transfer paste like I told you to? This only takes very little time, it is easy to do, and if done properly I'm sure your issues will stop. Make sure when reattaching the heat-sink it fits properly, so it is flat against the CPU surface. I've had issues with models that were difficult to properly attach, for some the orientation is important. If it isn't attached properly it can take very little time for the CPU to turn off. To turn the PC back on quickly remove the mainboard from the power-supply.

Sounds like you definitely have a faulty MoBo - the computer should not shut down after only a minute for any reason. My only other though is power supply, do you have another one you can test? If not, I would consider cutting your losses with this MoBo...


rindi - I removed all traces of the old thermal compound from both surfaces and then reapplied a little drop and then spread it around as you suggested.  I was about 5 minutes into repairing windows and it has just shut itself down again.

I guess I could buy a new mobo + processor and reuse the rest of the bits.... However if it turns out to be a problem with the power supply that money has gone down the drain!
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I would steal a PS from another machine or buy one of those first, you can always return it...
i think it would help to post some specs, mobo, RAM, GPU etc


Thanks for all the responses.

FlooringPro - I like the cut of your jib!  If my wife complains about the expenditure I'll just blame you :-)


I'm only glad i could help in the best way possible.  There's absolutely nothing like that new car smell !!
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