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Computer won't turn on


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#1 Flascher

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Posted 12 October 2011 - 03:58 PM

Hello, I'd like to thank everyone in advance for their help.

My problem started a couple days ago when I had plugged in my case fans (I had forgotten to when I finally got my first custom build working) and as soon as I had done that, my rig wouldn't turn on. I immediately tried unplugging the fans again to see if that had somehow made a short circuit or something of the sort. Unfortunately the computer still won't turn on. I've made sure my 24 pin ATX cable and my ATX 12v cable are securely plugged into my motherboard, all the 6 pin cords are plugged into the PSU correctly.

I'm not sure if it helps, but I did see the power LED turn on for a very short time and turn off and not flick back on again until I unplugged the PSU and messed with a few things. The power button itself did not turn it on though. I am worried that my PSU somehow fried.

Any ideas as to why my computer won't turn on?

Computer hardware: (not sure anything is of interest to this topic aside from possibly the PSU and motherboard.)
Motherboard: Gigabyte GA-990XA-UD3
CPU: AMD Phenom II X6 1100T Black Edition Thuban 3.3GHz
RAM: G.SKILL Ripjaws Series 8GB
PSU: OCZ ModXStream Pro 700W Modular High Performance
SSD: OCZ Solid 3 SLD3-25SAT3-60G 2.5" 60GB SATA III MLC
Video Card: SAPPHIRE 100338L Radeon HD 6770 1GB 128-bit GDDR5
Case: NZXT Phantom PHAN-001WT

Thanks again!
~Flascher

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#2 Nicholas Basso

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Posted 12 October 2011 - 06:54 PM

When you opened up your case to install the case fans, is it possible you bumped or dislocated the connector for the power switch to the mobo front-panel header?

Have you tried just shorting those two pins with the case open and all plugged in to see if anything changes?

Finally, make sure your CMOS reset jumper isn't accidentally set on. Not sure why, but still.

Coulda been a short or something, but check those things first I guess.

When you plug in the cable and say the power LED flickers do you mean the one on the front or is there one on the board?

Also, you're unplugging and plugging in the 24-pin with the PSU powered on? Tsk tsk.

#3 Flascher

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Posted 12 October 2011 - 08:46 PM

When you opened up your case to install the case fans, is it possible you bumped or dislocated the connector for the power switch to the mobo front-panel header?

Have you tried just shorting those two pins with the case open and all plugged in to see if anything changes?

Finally, make sure your CMOS reset jumper isn't accidentally set on. Not sure why, but still.

Coulda been a short or something, but check those things first I guess.

When you plug in the cable and say the power LED flickers do you mean the one on the front or is there one on the board?

Also, you're unplugging and plugging in the 24-pin with the PSU powered on? Tsk tsk.


Thank you for the response. A lot of useful tips in there, although I'm not sure what "connector for the power switch to the mobo front-panel header"?

Shorting what two pins?

Could you possibly point out where the CMOS reset jumper is?

I hope it wasn't a short, more than likely lotsa things would be damaged (probably the mobo)?

When I plugged the cable in to the back of the PSU, the power LED only turns on sometimes. Most of the time it doesn't.

Oops... How embarrassing. I wasn't aware that doing such a thing could cause problems. I hope it hasn't resulted in/cause any major problems in the future.

Thanks again!

#4 Nicholas Basso

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Posted 13 October 2011 - 06:11 PM

Thank you for the response. A lot of useful tips in there, although I'm not sure what "connector for the power switch to the mobo front-panel header"?


On a computer case, you have your power button on the front. This is a pushbutton switch which has, typically, two wires coming out of it, coming to a small black rectangle with two holes on it.
Many of the other parts, such as power LED, reset switch, HDD LED, etc, have similar things, though some use three, and it varies from system to system which ones you get.

On your motherboard you will have something called a "front-panel header". This is a term for a group of pins, usually 2 wide by some-number long, which are where these little connectors (the black rectangles) get plugged into. When you push the power button, it makes a momentary connection (or short) between the two pins for the power switch, thus telling the motherboard you have pushed the button, and triggering the power on, power off, standby, or whatever behavior is appropriate given the current state of the computer.

Shorting what two pins?


See above.

Could you possibly point out where the CMOS reset jumper is?

It varies from system to system. If you're completely unsure, you may be able to find reference docs for your motherboard online - if you built the system yourself or the system was custom built, the motherboard may have a manual. If it was a big-box build (Dell, Lenovo, what have you), then you may need to search online to find one of those, or call the manufacturer.
Note: Some motherboards work differently and do not have such a jumper or reset.

I hope it wasn't a short, more than likely lotsa things would be damaged (probably the mobo)?

When I plugged the cable in to the back of the PSU, the power LED only turns on sometimes. Most of the time it doesn't.

Oops... How embarrassing. I wasn't aware that doing such a thing could cause problems. I hope it hasn't resulted in/cause any major problems in the future.


Well... huh.
If it was a short, there may be some bad power going on.
Again, are you indicating you plug the power into the computer and the LED on the front panel comes on, or is there another LED on your motherboard for power (some motherboards have it as a diagnostic/troubleshooting feature). Does it stay on or come on very briefly? Does it flicker?

Finally, doing ANY work inside your computer which involves connecting or disconnecting cables or power lines is BEST done with the computer off, the power out, and you being properly grounded with the case.

If you're unsure of how to do so or any other steps from here, my best recommendation becomes a local technician, who may be able to power-test the PSU or the motherboard.
While I dislike telling people not to help themselves, in this instance you're starting to see possibilities of electrical shock if you play around too much (it's very unlikely, but still).

I, unfortunately, am not an electrical engineer, or I could give you better advice - this is more diagnostic of "What happened" rather than "how to fix" -- because chances are if you're getting no response from the power button, and the section about the motherboard front-panel header doesn't help, and we can't find the CMOS reset, it's kind of a guess and chances are we're looking at hardware failure.

If you post the model of your computer here (assuming it's a brand name/big-box), somebody might be able to reply with the instructions on those steps -- I wouldn't know though myself.

---

Sorry for the disjointed nature of my post, it's hard to do when you're doing this on available time on the local service desk ;)

#5 Flascher

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Posted 13 October 2011 - 10:41 PM

-useful information, snipped to save some space- :)


Thanks so much for the response!

I have checked the POWER_SW connector (or as mine is labeled, and I assume that this is the connector you are talking about) and it is securely plugged in and in the right spot. I also failed to mention that the Power LED on the top of my case goes on for a short amount of time. It doesn't flicker or anything. It just goes on once for a split second, and then won't go back on. I also have a friend that is a computer science major and is also studying electrical engineering, so I think he may be able to help me if I can't figure out what's going wrong. Your post was well organized, don't worry about that. I just appreciate that you responded to my problem. :)

Thanks again!

EDIT: Also, my computer is a custom build, I have the hardware I used in the original post. Hope that helps!

Edited by Flascher, 13 October 2011 - 10:42 PM.


#6 westom

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Posted 14 October 2011 - 09:33 AM

... I did see the power LED turn on for a very short time and turn off and not flick back on again until I unplugged the PSU and messed with a few things. The power button itself did not turn it on though. I am worried that my PSU somehow fried.

Power button does not turn on power. That button (and many other functions) is monitored by a power controller. Controller decides when power is turned on or off. And if the CPU is even permitted to execute. You must provide numbers for the power controller and all other power system components to first identify, then fix that problem.

Buy or borrow a multimeter. A tool so simple as to even be sold in Kmart.

Set the multimeter to 20 VDC. Connect its black probe to the chassis. Touch the red probe to a purple wire where the PSU connects to the motherboard. Meter should read about 5 volts. But report all three digits. Repeat same for a green and gray wire. Report numbers before and as the power button is pressed. And finally monitor any one red, orange, and yellow wire as the power switch is pressed. Note any rise and final voltage number on each.

Post those three digit numbers. Relevant components will be accused or exonerated in a next reply without speculation based on those hard numbers. Do not bother suspecting anything else until the power 'system' is first exonerated.

#7 Nicholas Basso

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Posted 14 October 2011 - 06:44 PM

Oh right I'd forgotten that you posted your hardware early on.

I'd check for a CMOS reset instruction in the manual for your motherboard, be careful about whether it says to do it with power on, off, etc.

When you press the power button after that flash of the power light, nothing happens at all?

If the power light comes on I would suspect the PSU is functional, though it could be that it's not providing enough power - maybe if your friend has a power supply tester or even a voltmeter/amp-meter (and a proper amount of knowledge about how to use it with a PC PSU) he may be able to verify the PSU's sustainability. Failing that, if manually shorting the two pins that the Power_SW connector is going across (just in the rare but possible case that the power switch itself is faulty in some way)... if shorting those two pins manually (paperclip or thin bared wire) does not power on the PC it may be a damaged motherboard, in which case you might be able to get it RMA'd on warranty from the manufacturer. I'd suspect the deadline has passed on the reseller's return policy, though.

Sorry for the bad news.




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