Computer suddenly shuts down then black screen no beeps upon reboot (could be psu, motherboard, cpu?)

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Scyvh

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(when I registered I made a lengthy post, which seems to have disappeared somewhere in between registering and activating; please let me know if you find it,)

(could be motherboard, psu, cpu)

Dear all,

A longtime lurker, who always found a solution to any software or hardware problem here. But the following problem is beyond the scope of me and all of my hardware savvy friends. Let me stress that we have not succeeded in reproducing the problem, which has made pinpointing the problem very hard, because it seems to happen at random ánd is unreproducible.

PC (windows 7)
Asus P7P55D
I5 760
Coolermaster heatsink (hyper 212)
Corsair OCZ 700w modulair
Asus GTX 460 directcu
4gb of RAM

Beginning
The problem first occurred a number of months ago. Whenever the pc went into standby mode, it would shut down itself. Then when rebooting, only a black screen, no beeps, no post, (red CPU light though), fans blowing and lights on as well, and only willing to reboot properly until it had ‘rested’ for a few minutes. Then everything would be fine. This only occurred when going to sleep/standby, so our solution was to simply turn that off.

Fast forward
The problem started to recur again after a few weeks. Now it manifested randomly; when surfing the internet, when using Word, but also during games. It became almost reproducible when playing Starcraft 2, guaranteeing the shutdown. Since SC2 is CPU intensive, we suspected that.
However, the PC ran any stress tests (OCCT, Furmark) without flaw; the problem did not occur. The only test that reproduced the problem was OCCT’s PSU test, stressing the PSU. There was a little bit of dust there, and when cleaned out the PC could run the PSU stress test, and SC 2 flawlessly again.
Until the problem returned.

Now, the problem again occurs more regularly, but still at random and not reproducible. We have done a number of things to try to find it, but all to no avail (please see below).

Installed an SSD with fresh windows 7 install
Checked all the fans / cleaned any dust
Cleaned heatsink, removed and reapplied thermal paste
Followed all steps in “pc won’t go to post” thread
Removed and returned components a number of times
Removed a slight overclock on the cpu (from 3,3ghz back to 2,8)
Reset the bios
Updated the bios
Checked the DDR memory

The system runs quite cool, with temperatures of the CPU and GPU being around 30 when idle, and 50 (CPU) and 60 (GPU) under stress,

I hope you will be able to offer any suggestions to follow up through.
 
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pcgaming98

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You removed and returned a couple of components? Does this include the CPU and motherboard?

It can't be a motherboard issue, sounds more like your PSU is dying (hard to believe, Corsair is top dog in the PSU biz but it's possible). Since you're a tech savvy guy, you have other PSU's lying around right? If you do, try testing them out, see if your computer randomly shuts down.
 
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Scyvh

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Thanks for your quick reply.

I would definitely not call myself tech savvy, but I am able to do most basic hardware stuff and good in looking things up. That's why I have had 3 friends who know their way around hardware and build their own pc's look into it. We first suspected the thermal paste (perhaps some part had come off during the years) because of the irregularity of the problem, but we know for sure it can't be that now.

Both the PSU and the motherboard are currently my prime suspects. We don't have any spares of those (I think I could grab a corsair 500w from a friend though, that should be enough). The red CPU light on the motherboard burning during a shutdown worries me a bit that it could be the motherboard. But from what I've read, if it's a psu or motherboard fail, the problem should occur much more often, or the pc should simply permanently refuse to go into post.
 
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pcgaming98

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I'd first try looking at getting that PSU from your friend. The thing about the CPU light is, it could be flashing red because the CPU can't start up due to lack of volts. The PSU could be failing to give the right amount of voltage the processor requires. If your friend's PSU also doesn't help, I guess it actually is the motherboard after all.
 
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Scyvh

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I will check the psu. Are there any other suggestions? Since I've been trying to get the pc to work for a while, I will use the coming days for one last try, before sending it off to a pc repair shop.
 
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pcgaming98

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It looks solely like a PSU problem. If it was the motherboard, the computer wouldn't even start and if it did, you'd get no display since the sockets the components are plugged into are all bad. If it was RAM, you'd still get no display. If it randomly shuts down, and your system isn't overheating, it can only be one answer.

Also, you dont necessarily have to pay to see if it's the PSU. If the tech repair shop guy is nice about it, he can let you use a spare PSU to see if it will start the computer up. The only time you should have to pay is when he actually repairs the thing (which is most likely by buying a PSU from him, which I dont recommend, he'll probably overprice it).
 
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Scyvh

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That's solid advice. I will go there tomorrow.

I have understood that there is no software to adequately test whether the PSU is malfunctioning. However, in CPUID HWMonitor there is one voltage fluctuating constantly; the CPU VCORE (it fluctuates between 0,896 0,912, 0,944 upwards to 1,208 V ). Would that be any indication? (the other voltages listed don't fluctuate at all).
 
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pcgaming98

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That's still an indication that the PSU is failing. It's giving the CPU lack of voltage, one minute it's giving the correct amount, one minute it isn't. That's why they're going all over the place.

Funny that it only does this for the CPU though. This starts to make me think a bit. A bad CPU CAN make your system shut off, so that's something I'll have to look into.
 
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Scyvh

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Update:

The pc has been at a (good) pc repair store in the city. Unfortunately, they've had three of their hardware experts look into it, and they have not been able to reproduce the problem (they ran several tests, overnight as well). They have checked each individual piece of hardware, double checking the PSU, and found nothing (everything is functioning as it should).

I would much appreciate any new options I haven't considered yet to look into.
 
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Scyvh

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They did, and they also checked the old psu itself. I have another update.

Update 2:

One of the hardware people spent another day with the pc, running a bunch of programs to analyze each and every part, and swapping them as well. In the end, he was finally able to reproduce the problem, when running tests on the motherboard it self. He's quadruple checked all hardware components which are all working fine, but can't pinpoint anything particular on the motherboard. Since they can't order the old socket 1156 motherboards anymore, I'll have to go look for one.

Might just go for a new one now.
 
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Scyvh

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Would have to be a new (used) 1156 motherboard, since they couldn't pinpoint what was wrong on the motherboard (only that it must be the motherboard).

Thanks for all your help pcgaming98!
 
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Scyvh

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It's actually much harder to find one (new is out of the question), even second hand (most come coupled with a cpu). Depending upon how long it takes, I will either get the motherboard or an entire new pc first. I can always sell it along later on.

Thanks for all your help!
 
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Scyvh

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Update

Unfortunately, I am in need of some expert knowledge again. I found a used motherboard, and for 1,5 month the pc ran flawlessly, before the problem appeared again two days ago, culminating in another sudden shutdown (and refusal to reboot) yesterday.

I'm not very hardware savvy, but that the pc functioned properly with the new motherboard for such a time and only now shows the old problem again, seems to imply I have to look for something else. But I'm at a loss what for, the pc's been at my city's finest pc store where they spent a week testing every element, finally concluding only the motherboard could be at fault.

I'm looking for fresh ideas on how to fix this.
 
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pcgaming98

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If it happens twice to two different motherboards, and two different power supplies, I am pretty stuck myself. I'm currently at school, so I can't research as much as I'd like to (apparently half of the computer tech sites are considered "adult"). But I will look into this.
 
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Scyvh

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Update:

Today a friend checked the psu with a multi meter. Turned out fine (ratings of 12,4), but when he touched the back panel of the pc when it was shut down (outside the case, where the ventilation for the psu is) he got a 200 volt shock. Inside, there's nothing wrong with the psu.

The voltage drops when read, so we think this explains why the pc after having shut down needs some rest.

Is a faulty psu the now logical conclusion? Or could something else cause this?

Thank you for your help.
 
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Scyvh

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Update: a new psu gives the same situation. 220 volt on the back of the pc case.

The pc is connect alone on the power (ungrounded) socket. Connecting it to a grounded socket removes the current, but not the will-not-go-past-post problem.

What could cause the 220 on the case?
 
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norsestar

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Both PSUs probably have filter circuits with capacitors between hot and ground. When connected to a grounded outlet, the capacitor current flows to/from ground and the case voltage stays 0. When ungrounded, the case voltage floats at line voltage (220V for you). (I discovered an improperly grounded outlet this way myself...) For your safety and the computer's, you need to use a grounded outlet.

I wouldn't expect an ungrounded outlet to automatically fry the motherboard but it would certainly make it more likely to be damaged. This would explain the short lifetime of the first motherboard and probably the second. Sorry to say, but I'd try another motherboard and make sure the system is always plugged in to a properly grounded outlet.
 
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Scyvh

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It's an OCZ modxstream pro 700, and a corsair cx500m.

The way I understood it, when ungrounded there would be around 120 volt rather than 220? I have not found any examples online of a case with 220 on it.

I can look for a third motherboard, but I'm a bit worried that if I ground the pc (I will) I will have solved a symptom rather than the direct cause?
 
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norsestar

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The voltage you'd get on the case would depend on the line voltage and how things are wired.

We don't know if grounding will fix the underlying problem or just a symptom. We don't even know for sure that the motherboard is the problem without swapping it out (or swapping everything connected to it to see if the problem moves), but I think that's the most likely since you've already swapped PSUs and replacing the motherboard fixed the initial problem. I wish I could be more sure but that's the best I can do with what we've got.
 
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Scyvh

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You've helped a great deal. Tomorrow, we are going to do a final check on the pc and the wall socket itself, making sure that nothing is wrong in the pc itself. Grounding has removed the current, even if only a symptom it seems a lot safer not having the current there.

I'll have to give it a thought whether it is worth getting another motherboard, or whether buying a new pc would be more cost effective. First things first though, and that's to find out where the current comes from tomorrow.
 
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Scyvh

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A final update: over a month further on, the problem hasn't occurred again. We discovered that the current coming from the wall socket was normal (0 on the pc when off, 110 when on), but connected to the wall socket was a separate socket box, where the pc was plugged into. That box had an on/off switched. If it was turned on, it gave 110 on the pc (normal behaviour), but when turned off it gave the 220 (it should give 0 then). We tried several different socket boxes, but they all reproduced this problem, so something might be wrong with the wiring in the wall itself.

For now though, the solution has simply been to plug the pc itself directly into the wall socket, and all other peripherals into the socket box. That's been working for over a month now.
 
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