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Computer starts automatically and then it won't turn back off!

Last response: in Systems
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May 22, 2014 12:40:36 PM

This just happened after i assembled and installed clean Windows 7 64 bit , installed latest drivers for both motherboard and graphic card on newly assembled desktop with the following specifications:-
Gigabyte B75M D3H Motherboard
Intel Pentium G2020 Processor
PowerColor R7 250 1GB GDDR5 Graphic Card
4GB Simmtronics Ram
500 GB Hitachi HDD
CoolerMaster Thunder 450W

The problem is that the moment i flip the switch on my PSU to "On" , the computer powers on without the need to press the specified power button on the cabinet. As this is not a big issue as i don't think it as a big problem i thought to leave this as it is but after i did the work what i wanted to do on my computer i thought to shut it down through Start menu->shutdown , it went on the usual way (successful shutdown) but after 4 seconds of "no glow light" indicated and fans went off but the computer turned on automatically again(usual way with no errors) without the need to press the power button and boots to windows 7 normally. And i have to quickly jump to unplug the computer safely and correctly in those 4 seconds to completely switch it off.

I checked the power- and power+ pins on my cabinet and othe pins too but they are exactly there where they are supposed to be(checked according to the manual) , i have also checked the setting on BIOS (ac back) it is set to "always off".

1)I havn't updated windows (as i don't think it would be a software issue because whenever i do any task on my computer it acts normally (no errors or problems).Assembled alot of systems for some companies and individuals but never usually updated windows and they didn't faced any problems without windows update and i myself facing this strange problem.

2) i haven't Re-installed BIOS.

What can be the problem and how do i get rid of it ?
May 22, 2014 12:47:30 PM

Your power switch might be shorted closed. Disconnect it and see what happens. If it does not turn on, check the switch wiring for that short. If it is in the switch itself, you'll either need to give up the reset function and use that switch (they're both momentary-on pushbuttons, so are electrically interchangeable) or replace the switch or your case.
For future safety if you upgrade in the future, do not consider your PSU as good for any more than 400W max; CM's "budget" PSUs have a history of issues from inefficiency and overrating to missing protection circuits.
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May 22, 2014 1:06:06 PM

Are you talking about cabinet power button to interchange with reset button through their respective pins?
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May 22, 2014 1:12:23 PM

Yes.
Also, since you mentioned "power -" and "power +" pins, make sure it is not the power LED that you connected where the switch should go. The switch has no polarity, but the LED does.
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May 22, 2014 1:17:42 PM

The led pin is indiacated with written "pwr led" and switch is indicated with "pwr swt" , so basically on that part i haven't made any mistakes and buddy i have experience of doing the same for many years but what can i do next? And thanks for replies
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Best solution

May 22, 2014 1:27:44 PM

Ok; I've seen poorly labeled connectors on some cases. Disconnect the power switch wires. If it doesn't turn on by itself, but will turn on if you short the pins with a screwdriver, then either the wiring or the switch is shorted. I once bought an Apevia case on which a factory drone (i.e. untrained idiot) had run a screw through the switch wires. Check the wires for abrasion, especially at any pinch-points.
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May 22, 2014 1:36:31 PM

I'll try that tomorrow and thanks but anything else i should do about it?!
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May 22, 2014 1:54:32 PM

If the PC still turns on with those wires disconnected, then I'd suspect the PSU.
If the switch and wiring test good, check for a loose screw or other debris trapped under the motherboard. Otherwise, nothing else comes to mind. Having built PCs before, I'm sure you know about using standoff or raised bumps, and only placing a standoff where there is a mounting hole.
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May 22, 2014 2:03:34 PM

I am also suspecting a defective psu :fou:  just have had this problem first time and don't know whatbi can do about it!
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May 22, 2014 2:07:09 PM

I gave that answer as best solution because it was exactly what i thought to do about my new problematic computer! But please other people also help me to get rid of the problem.
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May 26, 2014 3:12:48 AM

Onus said:
Ok; I've seen poorly labeled connectors on some cases. Disconnect the power switch wires. If it doesn't turn on by itself, but will turn on if you short the pins with a screwdriver, then either the wiring or the switch is shorted. I once bought an Apevia case on which a factory drone (i.e. untrained idiot) had run a screw through the switch wires. Check the wires for abrasion, especially at any pinch-points.


I have changed the cabinet and the problem solved. So, the power switch of the previous cabinet was shorting! Thanks for all your suggestions.
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