PC doesn't boot

[Devil_H@ck]

Hi,

When I came home today my step-sister told me that my pc wouldn't start anymore. She had been browsing the web a bit and then had left it on. About 3 hours later she heard a small 'pop' noise and the pc shut itself down. All that time no one had touched the PC.

At first I thought it was a cap that had exploded inside the power supply, so I took it out and tested it. Well, it worked just fine, so I put it back in.

When I press the power button, I can see the power supply start spinning for about 0.5 seconds and then it just shuts down and nothing happens anymore. I can press the power button as much as I want to, just nothing happens. When I remove the power chord and then plug it back in, it starts all over again: 0.5 seconds fan on, then everything shuts down again.

Does anybody has any idea what could be causing this? The pc was working just fine, well, except for one blue screen saying something about an error in the registry, but that can't have anything to do with it, since the pc now can't even get to the POST sequence.

Help!

[Ignite]

Check the power supply capacitors on the motherboard, frequently they are to blame. If you can test the psu with another motherboard that would be helpful. Some computer stores (such as the one where I work) will test your powersupply for free.

Many pc power supplies when presented no or very little load will exhibit the 1/2 second fan spinning up then nothing.

70% chance it is your power supply, 29% chance it is power supply related but on your motherboard, 1% chance it is something else.

[Devil_H@ck]

Originally posted by Ignite
Check the power supply capacitors on the motherboard, frequently they are to blame. If you can test the psu with another motherboard that would be helpful. Some computer stores (such as the one where I work) will test your powersupply for free.

Many pc power supplies when presented no or very little load will exhibit the 1/2 second fan spinning up then nothing.

70% chance it is your power supply, 29% chance it is power supply related but on your motherboard, 1% chance it is something else.

About that no load thing, when I tested the power supply by shorting the green wire to ground on the big mobo connector, there wasn't any load on the power supply right? Yet it kept running.

Then, when I put it in the pc it shuts down instantly. I'll check for cap failures on the mobo. Any idea how I should to that (except for seeing if they look burned)?

[nuppe]

Just in case...

If one of the components have blown (not on the motherboard), test it with a minimum config, even rip out the graphics card and memory.

If the psu doesn't shut down and the motherboard starts to beep, hopefully the motherboard is fine, and one of the other components have blown.

Otherwise, it pretty much has to be either the psu, motherboard or processor.

/Andreas

[Devil_H@ck]

Ok, I'll try that. Could also be due to the bios battery being all empty? (Which would be weird, since this pc is on for at least 6 hours a day normally.)

[fdegrove]

Hi,

Could also be due to the bios battery being all empty? (Which would be weird, since this pc is on for at least 6 hours a day normally.)

No.
Whether the PC is on x hours a day or x+n hours a day doesn't matter to the bios battery life.
When it nears empty state it loses date/time first, surely you'd have noticed that.

Try with a different mobo as suggested, I think the PSU itself is fine.

Cheers,

[Devil_H@ck]

K, I'll guess I'll have to get it to a PC store then, since I haven't got a 2nd mobo.

[dnsey]

If you feel like it, try warming the motherboard with a hairdryer, then booting. One of my PCs (which usually stays switched on 24/7) absolutely refuses to hard boot at room temp (PSU pulses like yours), but will do so quite happily if warmed a little.
I suppose I should track down the fault really, but a little heat is so reliable that I can't really be bothered!!

[Polimorph]

I think your problem is in the PSU, have a look inside and you'll see a resistor burned out, and/or a capacitor. I had this problem and I just repaced the bad component; now I can't remember what component was, but it took me little time to solve it.

[fcel]

While we're waiting for David H@ck's PC to come to live, I would like to post my version of the problem ....

I have a Pentium II PC which is about 6 to 7 years old. Recently it has develop a problem of not being able to boot up on first try. I'll describe more in detail below.

1) When I first turn on the computer, it will shut off after a few seconds.
2) I then press the power button a couple time and then the computer will start booting up again.
3) After a few seconds, it'll shut off again.
4) I then repeat step #2.
5) Sometime, it will boot up after a couple tries.
6) Sometime, it will boot up in safe mode where I have to reboot again so that it's in full boot mode.
7) Once it's booted up, the computer will stay on and operational.
8) If the computer is left on overnight, it will not function anymore on the next day (I guess this is what you call "computer freezed") although the computer does stay on.
9) I have visually inspected the power supply - I don't see anything unusual.
10) I also don't hear any "high pitch" sound from the power supply for sign of bad capacitors.

I would like to stress that if the computer does boot up, it'll stay on and operational except for one case that I mention above.

What could be the problem? Thanks.