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have a 6 year old PC but it powers off randomly, sometimes it will take a few hours, or sometimes it won't happen at all

when it does happen, the system loses power, but the mobo power LED is illuminated

when i press the power button, the PC will not turn on again

to turn it on again, i need to flip the power switch on the back of the PSU until the mobo power LED extinguishes, turn on the PSU, and the 'on' button works again

restarting the PC shortly after it has powered itself off seems to increase the probability and frequency of it powering off again (sort of how you would expect a heat issue to manifest?)

what i have done:

getting annoyed with my PC shutting down while gaming etc i decided to get out the wallet to attempt to fix the problem, gives me a good excuse to update as well :p

Round 1: new processor with stock cooling, new mobo, new RAM (old ram discarded), new GFX card, meaning that the only hardware that has been kept are the PSU, HDD and the tower unit

and the symptoms are the same.. powers off randomly

so, round 2: added a case fan, bought an aftermarket cooler for the CPU; installed with new thermal paste, re-seated the GFX as far away from the CPU as possible, removed the side panel of the case to improve airflow

..and the symptoms are still there... :'(

i did think it was a heating issue, but ive exhaused every idea i have to cool the machine, along with the hardware above; my room has no centeral heating, its winter, and the unit is next to an open window!

so logic says the PSU is the culprit as its the consistent variable in all the builds

i guess the only thing left to try is forking out for a new PSU.. before i spend £50 is this the action you would recommend? if so why? (to help me understand the situ) if not then what do you think is the problem?

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First thing as I read your first lines of text was that your PSU is too weak. And at the end you say that you have changed everything except that.

Maybe it wore off over time so its capacity isn't as big as it once was or you have added parts (like hdds) that drain more energy than it is abble to deliver.

Either way your problem sounded like a PSU problem in the first place, especially that you had to flip the switch on the PSU to 'reset' it.

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Definitely the PSU! If it goes off and does not turn on with power button, its the fail safe in the PSU, over heat or over load protection. What size PSU you got 450watt? – ppumkin Jan 23 '12 at 14:50
This is it. Power supplies definitely get weaker as they age, often dramatically weaker. A 6 year old unit won't be able to push as much wattage as it was rated for when it was new. All those cooling changes will also draw more power and actually make your problem worse. – Joel Coehoorn Jan 23 '12 at 14:53
This answer is one weekend too late for me :( Flashed my BIOS in anticipation of a new CPU and now it's even worse. – MSalters Jan 23 '12 at 14:54
@MSalters don't worry - all that new cooling is just making your already taxed system draw even more power under load, thus exacerbating things. A new PSU should still fix you right up. – Joel Coehoorn Jan 23 '12 at 14:56
@JoelCoehoorn: Nice crystal ball there - it wasn't my question, but I too added cooling (scavenged from old PC). – MSalters Jan 23 '12 at 15:07

PSU's go bad, a lot. In fact, if it's not a HDD, it's typically the PSU. Also, you you have two parts from the old machine -- the CPU counts as well ;)! Take a look at your power settings in BIOS/or see if you can download monitoring software for your mobo. My old mobo (EVGA X58 Micro) had software that displayed voltages, temps, speed, etc. It was from this that I found out my voltages were a bit off (3.9 instead of 5). This can indicate a PSU starting to go bad.

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got a new processor, did that in round 1 :) will take a look at some monitoring software, not sure what im looking for though in relation to monitoring voltages; although got a feeling i might have useable data already in the form of graphs; i did a data capture over the network then the PC powered off when i thought it was temperature related – Gaz Jan 23 '12 at 15:45

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