Help diagnose dead computer
June 28, 2017 10:19 AM   Subscribe

I left town for 10 days with my (home-built, previously-working-fine) desktop computer powered off and the surge protector switched off but not unplugged. I came back and now it won't turn on. Please help me figure out what the problem is.

No fans start up, no lights come on, no POST, no beep codes, there's no indication that anything is happening. It seems really strange that it would just stop working completely while shut off.

I have tried a lot of troubleshooting and I'm just totally stuck. Here's what I've done:

- reseated all connections and cables
- tested the PSU using this guy: PSU is working
- tested CMOS battery: it is giving 3V
- unplugged all peripherals, devices and RAM, everything except for CPU and CPU fan: still nothing
- removed the power button headers on the case and manually shorted the pins to see if that cable was the problem: still nothing
- returned/replaced the motherboard: still nothing
- returned/replaced the CPU: still nothing

There's not even a light coming on on the motherboard to indicate that it's getting any power, but I'm not sure if the board has such a light anyway.

I am totally out of ideas. Having replaced the motherboard and CPU would seem to indicate that those aren't the problem. I wonder if perhaps the power isn't getting to the board somehow even though the PSU is working?

Any ideas would be much appreciated.


In case it's relevant, here are the main hardware components:

- ASRock H170M Pro4 motherboard
- Intel Core i5-6500 CPU
- Corsair Vengeance LPX 16GB (2 x 8GB) 288-Pin DDR4 SDRAM
- no discrete GPU
posted by number9dream to Computers & Internet (18 answers total) 2 users marked this as a favorite
You've tried everything I would have. Worth a shot though, try holding the power button down for 10 seconds with your power supply switch off. This will discharge any power left in it. Then try to power on normally.
posted by CoinOp at 10:29 AM on June 28, 2017

I'd be inclined to distrust the results of the power supply tester at this point. I'd see if you can borrow a known good, even if its lower powered psu to test if just the cpu, motherboard, & ram fire up without the rest of the components. On the plus side, power supplies are relatively inexpensive to replace.
posted by TheAdamist at 10:29 AM on June 28, 2017 [1 favorite]

I am so sorry to suggest this because it's probably the first thing you tried, and the PSU tester might imply this, but: is the power outlet working with other devices? The surge protector?
posted by supercres at 10:34 AM on June 28, 2017

Or the PSU-to-motherboard cable, though that might have been replaced with the rest of the MB
posted by supercres at 10:35 AM on June 28, 2017

To respond to the suggestions so far:

- the power outlet and surge protector are both working with other devices
- the PSU-to-motherboard cables weren't replaced, but both of them (24-pin main board power cable and 4-pin 12V ATX power cable) were plugged in to the PSU tester when I tested that, and if they weren't working then the circuit wouldn't be completed, right?
- about the power supply tester: I guess there could be something wrong with it, but I don't have a spare PSU, although I'm asking around to see if somebody I know has one
posted by number9dream at 10:49 AM on June 28, 2017

I might have missed this, but did you check the computer with a different electric outlet? or put a different appliance in the outlet to make sure the outlet hasn't shortcircuited?
posted by mirileh at 10:52 AM on June 28, 2017

Yes, the outlet and the surge protector are both working fine.
posted by number9dream at 10:53 AM on June 28, 2017

sorry, didn't refresh before posting
posted by mirileh at 10:53 AM on June 28, 2017

My desktop computer periodically doesn't like being plugged into one surge-protected outlet and won't turn on until I switch it to a different one, even though they both work fine. I know you said the outlet & surge protector are both working but you tried switching it to a different one right?
posted by bleep at 11:12 AM on June 28, 2017

Is the power switch for the PC itself dead? It’s been awhile but I had a situation like that and was able to jump it fine, the switch had just gone bad or something.
posted by sixfootaxolotl at 11:20 AM on June 28, 2017

I've tried several different plugs. I've also tried manually shorting the pins, so it's not that the power switch is dead. (Or at least, the power switch may be dead but that's not the main problem here.)
posted by number9dream at 11:21 AM on June 28, 2017

The power switch itself, or some other part of, or connection attached to, the case?

If you have access to another desktop machine, it might be worthwhile to debug this by moving components from one machine to the other, swapping them out one by one (as much as possible), until you gradually transform one machine into the other. Eventually, either the second machine will stop turning on, at which point you know you've introduced the error source to it, or it will work and be the first machine, at which point you have eliminated the problem.

One other thing to check: some kind of short that has destroyed the new motherboard also.
posted by amtho at 11:24 AM on June 28, 2017 [2 favorites]

I would still be very inclined to try with a fresh power supply. I can't tell you how many times I've had to replace a theoretically "tested and known good" power supply shortly after installing it.
posted by brennen at 11:26 AM on June 28, 2017

My vote is to try a new PSU as the next step.
posted by cnc at 11:58 AM on June 28, 2017

The lack of of any signs of life (i.e. POST, lights, beeps) almost guarantees that it's either the motherboard or the PSU. If it were RAM, CPU, HD, etc. it should at least show some signs of life before it shuts down again. Since you've tested this with a known-good motherboard in an actual real-life setting, I would urge you to actually test the PSU in a real-life situation (or, alternately, to replace it with one that you have verified works in a known computer). I'm wondering if the PSU supplies enough power to show up as "good" on your tester, but flakes out when it's put under any real load.

Other (more quirky) possibilities: Have you tried replacing the cord that goes from the outlet to the PSU? Have you tried getting it to turn on by plugging it directly into an outlet and bypassing the surge protector (maybe the surge protector also fails under load)?

But, really. I'd put a small amount of money on it being the PSU.
posted by Betelgeuse at 12:15 PM on June 28, 2017

I'd bet it's power related too, and likely a bad PSU. But one thing that got me one time was a power connector that was very tight. It seemed to connect but it wasn't really connected until I sanded the male part down a little to fit the MB.

That was on a new build so I wouldn't expect you to have the same issue. But it could be an issue on the replacement MB.
posted by jclarkin at 1:25 PM on June 28, 2017

I also vote power supply. But... did you reset/clear the CMOS after making hardware changes? It's so simple, but forgetting it has messed me up more times than I want to admit.

However, I just dealt with an extremely quirky no-power issue on my ASRock Z77 Extreme4 with an i7-3770k. It seems that ASRock boards sometimes have weird issues after experiencing a loss of power. This buildapc Reddit thread has more details.

In my case, I tried many of the things you did, but I also replaced the PSU with a brand new one (after which, the PC worked fine for a day), and then I had the same issue reoccur after the first shutdown. Grrrr. Much testing later, I figured out that 9 times out of 10, pressing the power button does nothing, but if I reset the CMOS (my board has a button on the I/O panel, so it's easy) over and over, eventually, it'll come up. I'm currently still using the PC (which will randomly die here and there: no bluescreen, no errors, no warning) while I look for a new motherboard on ebay. I can't be absolutely sure that a new board will fix the issue, but replacing the MB was the best conclusion I could figure after days of swapping/testing of various components.
posted by snowleopard at 2:01 PM on June 28, 2017

Update: it was the PSU after all. I guess the tester I had was supplying the correct voltages but not a realistic current under load. Thanks for the suggestions, everybody!

For posterity, I had an interesting experience with a computer repair dude operating out of his house -- he had a spare PSU lying around to test with, and kept up a good monologue about his step-son being one of the first employees at **big-name tech company redacted** and retiring at 28 but no longer talking to him now, but he keeps up with his activities on facebook, oh hey don't sit on that my cat's ashes are in there, etc. Plus he gave me a bunch of CDs on my way out of bands that he had recorded.
posted by number9dream at 3:38 PM on June 28, 2017 [6 favorites]

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