Desktop Computer will not turn on. Why not?

[JordanIB]

Tried searching but nothing quite matched what I was looking for:

The symptoms: For a few weeks now, I've been having off and on issues with my computer powering on. I'd press the power switch and it wouldn't do anything. Often it seemed like I had to give my computer a "rest" for a while after shutting down before trying to power up again. In the last couple weeks, this has morphed more into having to hold in the power button for a couple second, pushing it in a certain place, and releasing it quickly, and hope that the machine powers up. As of last night, it is completely dead. Push the button and nothing happens. No fans try to run, no beeps, no nothing.

Does this sound like I just need a new power supply?

In googling, I've seen people mention the motherboard LED, so I'll just say that the green LED light on the motherboard is on, if that helps to diagnose.

What else can I do to figure out the exact problem? I've read about trying to short the pins on the power switch or something like that, but attempting something when I have no idea what it means makes me a little skiddish.

Any help is greatly appreciated.

[MisterW]

It sounds like it is most likely a power supply or motherboard issue. You said that "giving the machine a rest" seems to help. One cause of the problem could be bloated capacitor(s) on the motherboard. If this is the case, the computer would turn on normally, but either freeze up or not work after a short time. Turning it off, allowing the damaged capacitors to discharge, then starting up again would cause the machine to do the same thing. Turning it off and back on right away would result in a nearly immediate freeze/malfunction.

If this sounds like it could be your situation, you can open your computer and look on the motherboard for small, cylindrical shaped pieces (capacitors) and inspect them for a bloated shape. If you find suspect bloated capacitors, the motherboard is your most likely problem and you'll need a new one.

-MisterW

[BiPolar_Nut]

I mostly agree w/ the above post, with one alternative to suggest.

It could just be a worn out power switch.

To test the power switch theory, you'd do the "shorting it" thing which you may or may not be comfortable with. Basically, most of the front panel stuff (power and reset buttons, HD and power LED's, PC speaker) all plug in in the same general area on the mainboard. You;d need to determine which wire pair is for the power switch and short those 2 pins. Most mainboards have separate plugs each for the speaker, power switch, reset switch, hard drive LED, and power LED. You'd simply remove the 2-wire connection labeled "power sw" and use a knife or something to short those 2 pins. Other brands (like most dells) have one big fat connector with all those connections on one big plug. In that case it'd prolly be easier to get a couple pins (like from a new dress shirt), and pierce each of the 2 power switch wires and touch the pins together (this won't break the original functionality of the switch).

If shorting the pins works reliably....then you simply have a worn out power switch. (which personally I'd either rig w/ any kind of momentary SPST switch I had laying around or replace just the computer case, which could range from $15 to $250 depending on the design and features))

[JordanIB]

Yeah, based on the slow and steady deterioration of the power/boot situation over the last month, I'm thinking it might be a worn out switch.

I will try to follow these directions while poking around inside the computer and see if I am comfortable shorting. FWIW, in terms of computer setup, I bought all the part and a friend of mine built it for me.

Any links on the internet with any kind of directions on how to do this?

[BiPolar_Nut]

[ QUOTE ]
Any links on the internet with any kind of directions on how to do this?


[/ QUOTE ]

Probably not because it's really very simple. Since you bought the parts and had someone assemble it, I'd lay 90:1 that you have a separate 2-prong plug to the motherboard for the power switch contacts instead of one bulky all-in-one type plug some of the larger OEM's use (like Dell).

If you still have your motherboard manual (or can google one) then it should be pretty easy to determine which plug and pins are involved. If the computer is already off when you try to short the pins, you won't damage anything by accidentally hitting something else next to it.

There's a good chance either the motherboard or connector itself (or both) are even labeled.

[JordanIB]

Ok, so I found the pins where the power switch connects. All I'm looking to do now is simply find something to conduct electricity between the two and see if it starts up when I short it?

Because I think I just did that using a knife like you suggested, and nothing happened.

Sorry for being such an idiot when it comes to this stuff. Just want to make sure I'm doing it right.

[JordanIB]

[censored], now I'm totally confused.

I was going to take my roomate's PSU, but before that, I figured I'd try switching power cords.

Sure enough, it booted up just fine. I thought I was home free. However, just as Windows was about to boot, the system just shut down and won't boot now [img]/images/graemlins/frown.gif[/img]

Now I'm worried...

Is my computer frying these power cords or something?

[JordanIB]

Weird. Just switched back to the old cord and it boot on the first try. Will have to see if it stays on....

It's odd because the problem was never that the computer just died on me. It was always just getting it to boot after having shut down properly.

[BiPolar_Nut]

I've had motherboards go bad (like Mister W mentioned...bad capacitors that domed their tops) that behaved this way and sometimes unplugging the power connection to the motherboard, waiting for the LED on the board to go out, then re-plugging it got it to boot.

It'd be nice if it was the power switch, but if shorting the pins didn't do the same thing as pressing a properly functioning power button, you prolly have a motherboard or power supply problem.

Since it sounds like you can borrow your roomie's power supply, I'd try that and see what happens. Once in my life I had a bad motherboard that would insta-kill power supplies and I fried 3 before I figured that out, but that was an odd problem on much older hardware. There's some risk, but it's very minor. If I was working on it and I didn't see any bad capacitors, swapping a known good PS would be my next step. (or I'd put your PS in a known-good junker box...depending which was easier to get to)

[CORed]

The motherboard LED is not definitive in determining whether the problem is the motherboard or the power supply. I had a power supply fail on my Dell, and the motherboard LED was lit. I didn't have the intermittent type problems that you did. I just turned off the computer one day and it wouldn't turn on again. I looked through the Dell forums, and found that quite a few Dell's sold about the time I bought mine had had power supply problems. A lot of people had called Dell support, and been told that if the motherboard LED was lit they needed a new motherboards, and found that the new motherboard didn't solve the problem and then had to buy new power supplies. I replaced the power supply and have had no hardware problems since.