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Help: Computer not turning on but power light is

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July 23, 2010 1:29:57 PM

my secondary computer (aka ex-primary computer now used as an overweight stationary mp3 player) spontaneously turned off a few weeks ago and hasn't turned back on. At first, the power light would go on when I tried to turn it on and then stay on until I cut power, but now that doesn't happen any more. I thought it was probably a PSU problem and figured I'd get around to it eventually but wasn't worried because I have a better computer that I use for everything... until now!

Exact same thing happened to my primary/main/good computer... well, same initial symptom anyway... It turned off in the middle of me typing an email and won't turn back on. I immediately felt the CPU heatsync (I know how hot it feels to touch when it's well over 50 degrees Celsius and can tell it was nowhere near that as weird as that may sound) and I'm damn sure it didn't overheat (I never see it go over 35 anyway, I only know what 50+++ feels like because my old computer averaged 50-65 under load). Hours and hours of video games have never pushed my GPU over 47 degrees celsius and I wasn't gaming when it happened so I doubt the video card got too hot. The power supply feels pretty warm but it always does, I don't know if that's normal or not but it's normal for my comp. I don't really know what to do, all I've tried is unplugging it, plugging it back in, hitting the power button... and giving it time. The only sign of life is my mouse lighting up when I press power and the green power light on the front turning on, needless to say I really hope it's nothing serious and I want to get it back up and running ASAP.

any ideas?

system specs:
500w psu
core 2 celeron e1200 (1.6ghz)
2gb ddr2
radeon hd 4650 (512mb)
OS: windows xp pro sp3
let me know if you need want to know anything else
a c 84 B Homebuilt system
July 23, 2010 1:44:38 PM

You may want to give the exact model of the PSU, the motherboard and the RAM.

When you try to turn it on, do any of the fans (case, heatsink, PSU, GPU, etc.) spin up? Does anything else turn on? Have you tried booting without the GPU (removing the major stress from the PSU)?

You may also want to run through the troubleshooting guide linked to in my signature. That'll pretty much cover any problem that can cause a build to not boot.
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July 23, 2010 2:20:39 PM

mobo: asrock 4core dual-vsta
not sure about RAM
not one fan budges, as far as I can tell all that turns on is the power light itself and the mouse... monitor stays asleep, computer doesn't make a noise, all keyboard lights stay off and numlock does nothing.

thanks for the troubleshooting link I'm having a look through it right now... most of it looks like setup related problems, I should note that my computer has been running fine for a year and I didn't change anything before this happened. Doesn't turn on after removing my video card or with either one of my two memory sticks removed.
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July 23, 2010 2:28:14 PM

I'll check what RAM I've got when I'm back at home, this back and forth between a working computer with internet and my broken computer is a pain. I'm also going to jump start my PSU with a paperclip or something if I can find one... really hoping I won't have to use that breadboarding tutorial!

Also, I have a multimeter that I've never used and don't know how to but my mechanic friend says they are simple. If it's a PSU problem could it be easily diagnosed with that?
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Best solution

a c 84 B Homebuilt system
July 23, 2010 3:01:40 PM

To be honest, I have no idea. I'm not the best troubleshooter, so I can only really help with the simple tests. It certainly sounds like a PSU problem since absolutely nothing starts up, but I don't know any way to be absolutely certain other than to swap it out with a working unit and see if that fixes the problem.
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a c 122 B Homebuilt system
July 24, 2010 6:15:15 PM

The best way to check your PSU is to try to borrow a known good PSU. If you cannot do that, use a DMM (positive lead to colored wires, negative lead to chassis ground or black wires) to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

This checks the PSU under no load conditions, so it is not completely reliable. But if
it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU. You can measure (carefully) from the back of the main PSU connector.
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July 26, 2010 1:09:31 AM

Thanks guys, my comp is working fine now with my friends 400w power supply, so I guess mine crapped out. Can only assume this is what happened with my other comp too.

Is it normal for power supplies to get ridiculously hot, despite 2 large fans working properly? The back/top of my comp case (where the PSU is) has nearly (not quite) been so hot to the touch that it hurts sometimes, when the CPU temp is 33-43 degrees and the ambient case temp lower than that... I'm fairly certain that the PSU was by far the hottest thing in there.

...and since like 95% of the hardware failures I've had over the years were with power supplies (and not all of them were cheapo PSU's like the 2 that just died, one was pretty nice) I'm just curious if there's anything I can do to minimize the chances of this happening to the next one I buy. I do have surge protection in my splitter and my power strip but I've heard that doesn't do much, so are there better forms of surge protection? Are there other common causes for power supply failures other than electrical surges?
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July 31, 2010 2:24:28 AM

Best answer selected by eznajdj.
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