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Computer turns on and right back off

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a b ) Power supply
October 21, 2011 5:53:32 AM

I usually leave my computer on, but recently I decided to turn it off and a few days later I tried to turn it back on and it wouldn't cold start.

Long story short, I took pieces out one at a time until there were only a motherboard and the PSU remaining and it still wouldn't cold start. I tried it about 5 times without any changes in configuration and eventually it stayed on. As in, with the exact same conditions, I got different results. Sometimes the fans wouldn't even attempt to spin, sometimes for just a second, sometimes for as long as 10 seconds, but they kept going off again until about the 5th time when they stayed on permanently.

Another long story shorter, I put all the parts back in one at a time and every time it would come on and stay on after 5 or 10 times of pressing the power button every time it would go off. I am posting this from the "broken" computer, and with all the parts back in it is completely operational, it just took some time to get it finally on again with everything in it. There doesn't appear to be any errors at this moment and all the devices appear to be completely operational.

Anyway, I have some IT experience, but not primarily hardware related. In my experience, most of the time something is wrong with internal parts it is a PSU problem, but I just wanted to check with the experts and get some other opinions.

Regardless of any possible configuration I can do, the exact same thing happens.

I have little to know capacity to switch out parts currently, so I am mostly just looking for a gut feeling kind of answer from people.

I have had my PSU, a 700w FX700 GLN and my video card, an ATI hd4870 both for about two years I think, but the motherboard, processor, ram, and other internals were recently acquired in one shot about half a year ago. I have an 80gb sata HD dual boot drive with xp/ubuntu on it and a 500gb sata dvr hard drive for data storage. Both the drives have been around a pretty long while. The dvr drive about 2 years and the 80gb boot drive about 5.

Until this point, I have had no problems of any sort with any of the components either in the current build or any past build.

The processor is amd phenom 2 x4 840
The mother board is an asus which I am pretty sure is this M4N68T
Ram is 2x 2gb crucial ballistix
80gb sata boot drive is a seagate st350031
I think the 500gb sata dvr drive is from western digital
video card is ati hd4870
PSU is 700w FX700 GLN

I don't know whether my PC has an onboard speaker or not, I swear it has beeped at me before, but it didn't at any point during my recent testing, even without RAM in the PC so I am flying blind in terms of error messages.

No overclocking was done at any point on any of these items.

Anyway, I am leaning toward the PSU being the culprit (about 90%) and either the motherboard or the cpu (the other 10%). If you guys can think of anything else I can tell you to help you make an educated guess on this feel free to ask, otherwise just give your best guess as to what the faulty device is.

- Edit - I looked at the guides that are FAQd here and I did the tests that may have been applicable, but they weren't.

Thanks in advance.

More about : computer turns back

October 21, 2011 6:27:25 AM

from the sound of it, it sounds like a psu or mobo issue, but I would check out the psu first. Another possible cause of these shutting down issues is heat.
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October 21, 2011 6:35:32 AM

phatbuddha79 said:
from the sound of it, it sounds like a psu or mobo issue, but I would check out the psu first. Another possible cause of these shutting down issues is heat.


I would agree with the heat case. Sometimes, the CPU fan/heatsink may not be seated properly or correctly, making bad contact and thus heating up very fast. When the temp reaches a certain threshold, the computer turns off instantly to prevent damage. Try reseating the heatsink over the processor (remove it then put it back as if it was brand new).
a b ) Power supply
October 21, 2011 12:52:17 PM

I disconnected all the PSU cables when I was taking everything out one part at a time, so all of the cables have been fully reseated.

The place where the PC is located is exceptionally stable as well, so bumping/nudging/etc is unlikely to have happened to it.

I actually can't take my CPU fan off of my CPU. The liquid that sits between the CPU and the metal heat sink has completely hardened. I tried to take it off and it didn't move a millimeter even pulling quite hard on it. I also can't take both it and the CPU out at the same time because the release for the CPU is under the heat sink.

I guess the connection between the CPU and heat sink is about as solid as it can get. Even still, all the locks on it were re-attached.

While doing all of those things, there wasn't a single change in the behavior of the PC.

As far as heat goes, I could believe that there was some heat damage to some device. I am one of the kind of people who leaves the sides off of the case even though it disrupts the natural front bottom to top back, but I have been running computers like this for decades now without problems.

That being said, I generally refer to my video card as "the beast" because it is quite loud, even at pretty much idle. At load it really screams like a jet engine. It also needs two extra power connectors to it in order to supply it with enough power to operate. Those things weren't enough to kill my other motherboard that I had for a year and a half before this (in the same conditions), but the motherboard I have now was free with the processor and is about as low end as it can be while still fitting the internals above (only 2 ram slots, only 1 video card slot, etc). I could believe that the board was low end enough to where the parts fried it, but it doesn't "feel" like it to me. Partially because the board, even low end, is quite new and the PSU is much older.

The PC seemed like it needed fewer pushes of the power button to start when it was just the PSU and Motherboard that were connected (maybe 5) and many more when all the devices were attached (maybe 15 or 20).

Note they all have to be in rapid succession, immediately after the PC loses power.

If I wait like 30 seconds after a series of power button pushes then that pretty much resets the count like I hadn't already pushed it.

It is like the PSU only spits out a little bit of power every push and it goes into the motherboard and it isn't enough to wake it up, but there is still some juice that hasn't dissipated in the internals if I push the power button right after the juice quit flowing, and enough times of pushing the button kinda builds up enough juice to get it going.

That is kinda what it "feels" like is happening, which is also why I kinda lean toward the PSU being the problem child. It is pretty old now and it kinda feels like an old car battery does, like the amount of juice it can put out goes down by just a tiny bit every day and eventually it is low enough where there isn't enough juice to start the engine anymore, even with proper use and care.

When I got the PSU about 2 christmases ago it was off of ebay, so it wasn't even new back then, but until now I haven't had any problems with it.

Thanks again for the responses.
October 21, 2011 8:47:52 PM

When was the last time you dusted the interior of your computer? Dust accumulation does cause problems, including causing short circuits. Have you tried cleaning the inside of your computer with compressed air? A standard can of compressed air like you'd find at Wal-mart or something should do.
a b ) Power supply
October 21, 2011 9:25:34 PM

I do a quick spray every few months and every time I am manipulating internals, so for the purposes of my question the answer is yesterday.

I couldn't start the PC (or I probably could have if I just kept hitting the power button, but I didn't know it at the time) so I pulled out the computer, sprayed everything, tried to turn it on again (fail), and then started doing everything I described initially.
October 22, 2011 5:49:13 AM

Raiddinn said:
I do a quick spray every few months and every time I am manipulating internals, so for the purposes of my question the answer is yesterday.

I couldn't start the PC (or I probably could have if I just kept hitting the power button, but I didn't know it at the time) so I pulled out the computer, sprayed everything, tried to turn it on again (fail), and then started doing everything I described initially.


LOL, believe it or not I only clean out my desktops once a year and they all work fine, you remind me of my buddy who does it every 3 months. The only way I see that you need dusting every few months is if your environment is dusty which is a living hazard anyway. I don't think you mentioned in your first post about the PSU being pre-owned. Here is an affordable PSU that surely can power all your components and is quite efficient.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

If you want a bit more power for future upgrades, here it is
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
a b ) Power supply
October 22, 2011 1:55:00 PM

I may have forgotten to mention that until later.

My 4870 video card has two extra rails for power in addition to what it can pull from the board.

I am pretty sure the max draw on it is north of 300. I would be kinda worried about putting it in the hands of a 450 or 500 watt power supply.

Per this thread

http://www.tomshardware.com/forum/279391-28-power-requi...

the entry for 4870s is this

Recommended is a 650 watt PSU with one 6 pin PCI Express connector and one 8pin connector. 1000 watt PSU with two 6 pin and two 8 pin connectors is recommended for crossfire.

Thanks for the advice, though.
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