Tom's Hardware > Forum > CPU & Components > Power Supplies, PC Cases & Case Mods > Help! My PC won't turn on. I think it's my PSU
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iu2687   08-21-2006 at 03:25:59 PM

while i was gaming the other day, i tried to untangle my mouse and keyboard with my pc on. i unplugged the usb mouse and everything was fine. but when i unplugged the ps/2 keyboard and plugged it back in, the computer turned off. i pressed the power button to turn it back on but it would only stay on for 2 seconds and then turn off again. did unplugging my keyboard fry my power supply? i just bought a new Antec Truepower 550W from newegg a few weeks ago. i could have gotten a non-branded one at Fry's for only $50, but i payed twice as much for an Antec because i heard it's the best. if it's the psu that's fried then i'm disappointed. although, i would be grateful if it wasn't my hard drive, however, since i did not back anything up.

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jaguarskx   08-21-2006 at 03:40:36 PM
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This topic came up a while go. Unplugging and plugging a PS/2 keyboard while the PC is running is generally not a good idea. But I have to admit I've done that one or twice myself. There is a slight chance that while doing so you can screw up your motherboard because when plugging in the PS/2 keyboard, the pins may not be grounded properly.

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trixst4r   08-21-2006 at 06:05:14 PM
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If you have a simple multimeter and a steady hand, you can easily test out your power supply.

Look at your 24pin ATX connector with the "key" (that clip thing that hooks on) facing up. Then counting from the top left hand corner, count 4 to the right and it should be a green wire hooked up to that pin. Short that to the pin directly to the left of it ( a blackwire) but remember to have teh power OFF before doing that. Turn on teh power. Using a 4 pin molex connector from the power supply, put your ground probe to black. Carefully test the red and yellow pins with the positive probe. Yellow should be 12V, red should be 5V.

Google it up for better detail on how to do it but that is pretty basic to do.

But it sure does sound like a mobo problem :? .

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iu2687   08-21-2006 at 07:45:20 PM
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Quote :

This topic came up a while go. Unplugging and plugging a PS/2 keyboard while the PC is running is generally not a good idea. But I have to admit I've done that one or twice myself. There is a slight chance that while doing so you can screw up your motherboard because when plugging in the PS/2 keyboard, the pins may not be grounded properly.



you're right. when i unplugged the keyboard, everything was fine until i plugged it back in. my pc won't start but my motherboard LED light would still come on so i didn't know if it was the psu or mobo that was broken. do you think it screwed up anything else like my power supply/graphics card/sound card/hard drive? is there some way to fix my motherboard or do i have to get a new one? i need to get a new one anyways because its an old 754 socket with agp card slot. but the problem is that i just bought a new x850 pro agp card for it. i hope i can return it now. :?

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jaguarskx   08-21-2006 at 10:34:42 PM
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Quote :



you're right. when i unplugged the keyboard, everything was fine until i plugged it back in. my pc won't start but my motherboard LED light would still come on so i didn't know if it was the psu or mobo that was broken. do you think it screwed up anything else like my power supply/graphics card/sound card/hard drive? is there some way to fix my motherboard or do i have to get a new one? i need to get a new one anyways because its an old 754 socket with agp card slot. but the problem is that i just bought a new x850 pro agp card for it. i hope i can return it now. :?



There is a remote possibility that shorting out the motherboard could have fried everything. But that is a remote possibility. One way to really determine if the PSU has been shorted out is to borrow a PSU from a friend and see if you can start your PC.

The more like scenario is the motherboard is fried, and you need to replace it. If there is a local PC repair center near you, I would bring it over and have them check it out. Just to be sure all the other components are fine. Not sure how much it will cost to inspect a PC so you might want to check out local prices.

I suppose in the "best case scenario", only your mobo is fried and you'll be able to upgrade to PCI-e. That's assuming you can still return your AGP card.

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Boggerslosh   08-21-2006 at 10:55:15 PM
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I have had the same experience but I found the root of the problem to be very odd indeed.

After testing my PSU in another junk computer I had laying around I found it to be good. Maybe some other device is messing with my comp. I unplugged everything and tried to boot with only the OS drive, video card, an alternate keyboard, mobo, one stick of RAM, CPU (duh), and another PSU (even though I thought my original one to be good).

No such luck. I ended up swapping out RAM sticks, video cards and the PSU but nothing seemed to work. Eventually, I took everything out and put it back in. I was really tired of doing all this and by what turned out to be some divine providence I only put my mobo back in with 2 screws. It booted. Then I plugged in everything else one by one. Added hard drives. Check. Original video card. Check. Original PSU. Check. You get the idea...

So my only conclusion was that the screws were causing my computer to not boot. That or some really nasty dust bunnies. I put a screw in and BAM. No boot. Weird huh? I tried different screw combinations to no avail. I guess there was some sort of weird grounding going on.

If you are wondering, my case is a Lian Li PC-V1000. It is currently housing the somewhat modest hardware you see in my sig with only 2 screws holding it all in

:D

The moral of the story. Electricity is a very strange thing. Try to eliminate all possibilities one by one and you will surely find the root of your problems.

[Edit: Grammer]

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iu2687   08-21-2006 at 11:26:34 PM
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my brother's pc had a problem with the same symptoms once. but i'm not sure if it was the same problem. he turned it off before he went to bed one night and in the morning the pc won't stay on for more than 2 seconds, but the mobo light always remains on. he put in a new power supply and everything worked fine. i'm hoping my pc has the same problem as he does because then i will only have to replace my psu. i guess i will find out soon enough when i test another psu on my motherboard.

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iu2687   08-27-2006 at 03:51:50 AM
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Quote :

This topic came up a while go. Unplugging and plugging a PS/2 keyboard while the PC is running is generally not a good idea. But I have to admit I've done that one or twice myself. There is a slight chance that while doing so you can screw up your motherboard because when plugging in the PS/2 keyboard, the pins may not be grounded properly.



what do you mean by pins not grounded properly?

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Newf   08-27-2006 at 04:56:25 PM
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Odds on favorite is that your mobo is fried.

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jaguarskx   08-27-2006 at 05:43:37 PM
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Quote :

This topic came up a while go. Unplugging and plugging a PS/2 keyboard while the PC is running is generally not a good idea. But I have to admit I've done that one or twice myself. There is a slight chance that while doing so you can screw up your motherboard because when plugging in the PS/2 keyboard, the pins may not be grounded properly.



what do you mean by pins not grounded properly?

The PS/2 plug has lots of pins in it that is used to draw power and send information to the PC. One of those pins is used to ground the the keyboard so that there will not a short circuit. It's possible that when you plugged the keyboard a micro spark occurred before the gound pin was inserted. That micro spark could have caused damage to your motherboard.

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iu2687   08-28-2006 at 02:54:54 AM
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do you think resetting my cmos by changing the jumpers and removing the battery for a few minutes might fix it?

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Newf   08-29-2006 at 11:41:36 PM
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No, but it costs you nothing to try it.

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CompTIA_Rep   08-30-2006 at 12:24:05 AM
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Try pulling the CMOS battery and remove the power suply connection for a minute or so to clear out any short.

My vote goes to shorted motherboard though. Seen it happen more then enough times as a tech. If you buy a power supply localy from a store that has a nice return policy, you can at least test it for free.

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iu2687   08-30-2006 at 05:52:54 AM
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i reset the cmos by pulling out the battery and switching the jumpers for about 10 minutes. i pressed the power button twice and it still didn't come on. but when i pressed it the third time while holding the insert key my pc finally boot up and everything worked as normal. nothing was fried. i want to thank everyone who offered my helpful advice on this thread.

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