Computer Death!
January 25, 2006 1:11 PM   Subscribe

Please help me diagnose a dead computer. The missus' computer was just dead one morning. Pressing the power butten results in absolutely nothing.

When unplugging the power cord I can hear a very quiet noise fading from the power supply. I can reproduce that by plugging and unplugging the power cord. Other then that, nothing. Zilch. Nada. I have looked inside the case, but can't see anything obviously fried, disconnected or otherwise broken. I don't have any spare parts available, so can't really try changing components. Any suggestions for what I should look for?
posted by The Carolingian to Computers & Internet (13 answers total) 1 user marked this as a favorite
Silly question, the actual on/off switch, on the back, near where you plug in the power cord, is that on?
posted by Capn at 1:13 PM on January 25, 2006

Unplug everything from the motherboard. Plug it all back in. Try it again.
posted by Jairus at 1:13 PM on January 25, 2006

Response by poster: Capn: yep, I have thoroughly tested that possibility :)
posted by The Carolingian at 1:15 PM on January 25, 2006

The PSU (Power Supply) is probably dead. Alot of the time a power supply will die after you turn it off. You see this alot on servers that have been running for a couple years straight. Once you turn it off it no longer turns on. I'd try a different power supply in othe words.
posted by meta87 at 1:27 PM on January 25, 2006

Is it a Mac? There's a pretty standard fix for that symptom that works 99% of the time. Let us know.
posted by Rothko at 1:31 PM on January 25, 2006

The problem can either be the PSU (as meta suggested), the motherboard (worst case scenario), the physical on/off switch on the case, or the connections between them:

Look for the jumper that connects the power button on the case to the motherboard-- it's a fairly small cable. Has it come loose? Also, check the connector from the power supply to the motherboard.
posted by justkevin at 1:38 PM on January 25, 2006

Response by poster: meta87: PSU being dead is what I am thinking as well, but there is definately something going on in the PSU because of this noise I can hear whenever it is unplugged.

If something else, like the CPU, is fried, should the fans in the PSU start when the computer is turned on (providing of course the signal gets to the PSU)?

Rothko: no, it is a PC.
posted by The Carolingian at 1:44 PM on January 25, 2006

Is it, by any chance, a Dell Optiplex? I just dealt with a similar problem on several of our Dells. It does not sound to me like a dead power supply if you're hearing the power supply fan spin up. It sounds more like the power supply is okay and the motherboard is bad -- possibly a blown capacitor.

The machine doesn't "beep" at all when you press the button, right? That means its failing to POST (power on self test) and implies a board level component problem. Can you open it? If so, open it up, look for an LED soldered to the motherboard, and power it up open (if you are comfortable doing that). Tell us what color and state the LED has (ie: "it's dark" or "it's yellow and flashing" or "it's red and solid").
posted by The Bellman at 2:08 PM on January 25, 2006

P.S. To answer your second question, on most machines if the CPU is fried the PSU fans will still power up -- as will the motherboard fans.
posted by The Bellman at 2:10 PM on January 25, 2006

Can you be more specific about the sound from the power supply? If it's a fan you'll see the fan spin up and hear it humming. Sometimes I've had electrical components make their own odd noises that aren't mechanical in nature, but they're always very quiet.

But yea, it sounds like the PSU is dead. They're not too hard to replace as long as you can wield a screwdriver with at least a little aplomb. Fairly cheap as well, if memory serves, at least compared to replacing a motherboard or hard disk.
posted by cyrusdogstar at 4:19 PM on January 25, 2006

I think too many folks are jumping the gun here. I have seen this many times where simply leaving the box unplugged for a couple of hours is enough to fix the problem. Let the capacitors drain overnight, then plug it in in the morning and see how that goes. With luck, you'll be right as rain.
posted by kc0dxh at 7:44 PM on January 25, 2006

Response by poster: Thanks for all your comments. At work at the moment, but will try these things out when I get home this evening.

The PSU sound is definately not the PSU fan, as it I can see that it is not moving at all.

kc0dxh: nope, I left it unplugged for a couple of DAYS, and that did not help one little bit.
posted by The Carolingian at 1:12 AM on January 26, 2006

It's pretty easy to diagnose a dead ATX PSU if you have, or can borrow, a DMM (digital multi-meter). This page has a little color coded chart of the relevant signals voltages corresponding to the industry standard color codes for the wires in the main ATX 20 or 24 pin power connector. You can disconnect an ATX PSU from the PC entirely, and try powering it up by itself using the paper clip trick.

Of course, if you don't have access to a DMM, the cost of getting one is a significant part of the cost of a low end replacement PSU, which is why many people advise that if you are in doubt, just replace the PSU. If you decide to do that, some people advise that size and weight of the replacement unit matter. If you have a P4 based machine, you need to be sure to get a supply that has an auxiliary P4 connector, if your current supply has it, in order to properly power your system. Newer PSU styles should also provide direct connections for the newer SATA hard drive style power connectors, so you may want to consider that if you have or will be getting SATA drives.

You can put in a higher capacity unit than what you already have (see the sticker on your current supply for ratings before ordering a replacement), but you don't want to put in anything with lower ratings. These days, higher output supplies are fairly inexpensive, and it doesn't make much economic sense to put in anything less than a 400 watt unit, if you are keeping the machine. A power supply only pulls as much power from the AC line as is required to meet the demands placed on it by the computer, but better quality supplies contain PFC (Power Factor Correction) circuitry to minimize the reactive loads a PSU can present to the AC line at start up and when heavily loaded, so that they deliver high efficiency in all operating conditions. Whether you'd actually save enough money on power to make up any difference in cost of the PSU with PFC compared to one without, over the life of the machine, is a calculation you'd have to make, but it is a feature that provides some indication of the overall quality of a PSU. If you are looking to never, ever have to do this again, or may add additional upgrades later, don't cheap out on the replacement unit.
posted by paulsc at 4:31 AM on January 26, 2006

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