Have you tried turning it off and then on again?

December 31, 2006 5:20 PM

It's the oldest computer question in existence... My computer won't start. Help me.

I feel like I've tried all of the obvious things, but maybe someone will have something even more obvious.

I have a HP z545 Media Center PC. It was working fine today, no error messages, no warnings, nothing. I shut it down, and now it won't start up again. I've tried
1. Plugging it into different outlets
2. Switching out the power cable
3. Hitting it and yelling "Whyyyyy!?"

Pressing the power button has no response. The fan doesn't start, there are no noises of things trying to power up, there's no text on the front LED display. Normally, I'd think this meant the power supply is hosed, but there's a small green LED light near the power supply that comes on when it's plugged in. According to HP's website, this means the power supply should be good. We've tried everything here except for the final step of disconnecting everything and reconnecting piece by piece to find the problem. Any other ideas before we try that?

posted by MsMolly to computers & internet (13 comments total)

I feel your pain. Seriously.

If it's not your power supply, it's probably your motherboard then.

I had the same problem happen to me twice in the past 4 months. The first time, my motherboard died and I had to get it replaced along with a new power supply.

Two weeks ago, it happened again and apparently they installed a faulty motherboard. I got it at a local computer shop so they replaced it for free.

I'm sure someone else can chime in on what else you can do.
posted by champthom at 5:26 PM on December 31, 2006

The link on the word "here" was supposed to go to this page. Stupid HTML.
posted by MsMolly at 5:43 PM on December 31, 2006

Power supply sounds like the most likely culprit no matter what the HP site says.

The upside is that it doesn't sound like the drive is dead, so you can almost certainly toss it in another computer and save the data.
posted by smallerdemon at 5:49 PM on December 31, 2006

i have had luck with finding the jumper to reset the bios or pulling the bios battery. it may boot and give you an error to work with.
posted by thilmony at 6:19 PM on December 31, 2006

Do what thilmony says and reset the bios. However, this often requires the motherboard to be powered up and if that's not happening...

Some motherboards have a standby LED. Is it lit? Check the cables between the motherboard and the power switch; if loose, no dice. Check also the cable for the reset switch, in particular, try unplugging it. If your reset switch is dodgy, it can prevent power getting to the motherboard.

If the power switch is faulty, you can try using a paperclip to momentarily short the contacts on the motherboard (it'll be 2 adjacent pins) that the power switch plugs into.

Or it could be the PSU. Total deadness is not a common failure mode but it does happen if something on the primary (high voltage) side of the switching regulator fails.
posted by polyglot at 6:36 PM on December 31, 2006

Proceed with caution, etc...

When you have all the cables removed as in the link to HP, you can test the power supply by jumping two of the pins on the connector that plugs into the motherboard (it should be a 20-pin connection, possibly 24). This should override the start signal to the power supply and the power supply should start sending DC power to the various connections. You should be able to check the voltages at the connections with a voltmeter. You can find pinouts online or in your manual.
A quick and dirty check would be to leave a cooling fan plugged in. If you get no voltages at all, then the power supply is probably bad, or at least some components.
One caveat is that if you have a fan or another component that is shorted out or is stuck and possibly drawing too much power, your power supply may shut down.

Again, proceed with caution. When I do this I unplug the power supply, jump the pins with a sort wire, tape over the jumped pins with electrical tape, then plug in the power supply and switch it on. If you do not know what a voltmeter or multimeter is, you probably shouldn't be doing this.
posted by Yorrick at 8:26 PM on December 31, 2006

Based on my very anecdotal experience, sometimes a malfunctioning PS/2 mouse or any USB device can actually stop the computer booting. You might try unplugging all the cables from the case and then see if it powers on (but you've probably tried that already). The other likely culprit is a PCI card that is busted or hasn't been seated properly, so once you resort to opening the computer up, you might try disconnecting all the PCI cards first.
posted by zixyer at 2:10 AM on January 1, 2007

I am not sure this will help you, but my observations (based on 30 years of electrical engineering) is that 90%+ of all problems are connector related. Cards, chips, power cords, ribbon cables, all are potential failure points. The wiggle loose, oxidize, get dirty/dusty.

Also, dead devices USUALLY are easier to fix than intermittents. Since it was working yesterday, something like a spontaneous motherboard failure sounds unlikely.

If it were in front of me, I would disconnect the power cord and get the system unit on the dining room table, gain access to the inside, gently re-seat ever connector I could see inside... gentle wiggling. (Look out for sharp edges, but there is NO high voltage in the unit if it is unplugged).

Re-assemble and retest. If it works, back up FAST. If not, computer shop time.
posted by FauxScot at 6:32 AM on January 1, 2007

If the power supply fan isn't running, and the hard drive isn't spinning up, its almost certainly because they're not getting any juice from the power supply. A PC power supply produces a range of separate output voltages and it's not impossible for some of them to be working (the LED) and others not (the fan).

I'd suggest getting your local independent PC shop to see if it will start up OK from one of their bench PC supplies. This would only take a few minutes. If it does, you can buy a new power supply pretty cheaply.
posted by thparkth at 10:40 AM on January 1, 2007

Power supplies are the primary component that fails, and are cheap commodity items. I've been through this over and over -- it's always the damn power supply. Pull your old one out, go to your favorite independent PC shop (not Best Buy! not Geek Squad! not CompUSA!) and ask them for a replacement. Should be like $30, spring for the higher quality PS if they offer one.

But of course first try the simpler solutions above, like the PS/2 mouse thing. Good luck.
posted by intermod at 2:56 PM on January 1, 2007

That LED is quite possible indicating that there is power into the power supply, regardless of what hp's site says. Most likely, there is nothing coming out of the power supply. New ones are cheap and easy to replace, as noted above. Make sure you tell the computer shop dude what drives etc you have in your system to make sure you get one big enough.
posted by dg at 8:12 PM on January 1, 2007

There's one small thing that hasn't been mentioned:
many power supplies have a built-in breaker. If your power supply has a little (usually red) slide switch to go from 110v to 220v, try unplugging the computer, waiting a minute, switching it to the other voltage and back, and plugging it back in, testing, etc. I rescued a pc at our office the other day this way. It's so much fun to fix a problem in 10 seconds that everyone thinks will take all day.
posted by wzcx at 11:47 AM on January 2, 2007

Thanks for your help! It was indeed the power supply. I got a replacement and swapped it in and things are back to normal.
posted by MsMolly at 6:52 PM on January 12, 2007