[SOLVED] PC Randomly Switches Off and On, but...

May 15, 2019
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On random occasions (even under light loads) my PC will switch off, then switch on after about a second. This could happen a few times throughout the day, however:

- A while ago I traveled for about two weeks, so I didn't use my PC then. When I came back, the problem was gone for about two weeks. So, the PC was permanently off for two weeks (even plugged out) and the problem didn't show for two weeks afterward.

- About three weeks ago, I opened up my PC and cleared out some dust, etc. and for about three weeks I didn't have issues. Now, it is happening again.

When it does happen, it usually starts suddenly with high frequency: for example, for three weeks now it NEVER switched off and on by itself, however, tonight it suddenly did it 3 times already. It even did it once before even getting to the OS startup.

I have read about this quite a bit but I did not see any cases that match my PCs symptoms exactly. Also, I know that this is likely to be the PSU or the motherboard. I will probably buy a new PSU soon, but obviously I do not want to do that unnecessarily.

If anyone could give an explanation for why this happens the way it happens in my case, I would be very happy.
 

R_1

Judicious
Herald
"It even did it once before even getting to the OS startup. "
this here tells the tale. the PSU is failing.
random reboots are usually three things in this order, PSU, RAM, or software.
your tale describes a time when software and RAM are excluded from the equation. I have some remarks prepared for similar questions.
My canned random reboot Rant
Random reboots are usually caused by the PSU, the RAM or software AND in that order of likely-hood.
PSU - If you can borrow/swap a PSU for testing. sibling/friend you can swap out the PSU and each system will be testing the other.
RAM - run the system with one stick of RAM see if stability returns if not Test all the RAM with memtest 86 for five passes or overnight. if you get no 0 errors after more than five passes the ram is good. with the random reboots I would suggest running this test after the PSU swap or after the PSU has been cleared.
Software - Drivers or other issues can cause reboots. Boot to a linux distro on a USB drive. mint linux will boot to memtest86. you can run the OS from the USB and await reboot.
end canned rant
 
May 15, 2019
3
0
10
0
"It even did it once before even getting to the OS startup. "
this here tells the tale. the PSU is failing.
random reboots are usually three things in this order, PSU, RAM, or software.
your tale describes a time when software and RAM are excluded from the equation. I have some remarks prepared for similar questions.
My canned random reboot Rant
Random reboots are usually caused by the PSU, the RAM or software AND in that order of likely-hood.
PSU - If you can borrow/swap a PSU for testing. sibling/friend you can swap out the PSU and each system will be testing the other.
RAM - run the system with one stick of RAM see if stability returns if not Test all the RAM with memtest 86 for five passes or overnight. if you get no 0 errors after more than five passes the ram is good. with the random reboots I would suggest running this test after the PSU swap or after the PSU has been cleared.
Software - Drivers or other issues can cause reboots. Boot to a linux distro on a USB drive. mint linux will boot to memtest86. you can run the OS from the USB and await reboot.
end canned rant

Thanks for the response.

Do you have any guess as to why it would work for 2-3 weeks without any issues when I either 1) did not use the PC for an extended period of time (i.e. two weeks), or 2) opened it up and dusted it out?
 

R_1

Judicious
Herald
speculating here
1 faulty capacitors.
2 thermal creep short, the heating of the parts causes them to expand slightly, breaking contact triggering an off cycle, where the part cools and contact is made again.
3 poorly made PSU. what model are we talking about here, when did you get it?
4 a faulty power protection, the PSU triggering reboots to protect the system from out of spec power when the power is fine
5 out of spec power triggering the power protections in the unit
6 I hate electrical gremlins

replacing the unit for testing will answer the "is it the PSU?" question quickly.
short of a PSU autopsy and testing on the components therein I'm just guessing.

it is unlikely to be software, if no software has been loaded yet.
it may be the RAM but before the OS loads there is nothing there to trigger a reboot, which leaves power
 
May 15, 2019
3
0
10
0
speculating here
1 faulty capacitors.
2 thermal creep short, the heating of the parts causes them to expand slightly, breaking contact triggering an off cycle, where the part cools and contact is made again.
3 poorly made PSU. what model are we talking about here, when did you get it?
4 a faulty power protection, the PSU triggering reboots to protect the system from out of spec power when the power is fine
5 out of spec power triggering the power protections in the unit
6 I hate electrical gremlins

replacing the unit for testing will answer the "is it the PSU?" question quickly.
short of a PSU autopsy and testing on the components therein I'm just guessing.

it is unlikely to be software, if no software has been loaded yet.
it may be the RAM but before the OS loads there is nothing there to trigger a reboot, which leaves power
It's an Antec VP500PC. Pretty budget apparently (it's a custom built PC I bought about 3.5 years ago...didn't really pay much attention to the PSU). It's powering a GTX950 and an i3 4170.

There is an alternative power supply that I can obtain with some effort to see if it works, but then again, after only clearing out the dust and reconnecting a few wires, it worked for 3 weeks with this power supply, so I am not sure how long I would have needed to borrow the other PSU to absolutely confirm that it is the problem.

Thanks again for the help. Off to buy a new PSU then I guess...
 

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