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Computer won't turn on, power or motherboard?

Posted on 2004-10-19
Medium Priority
Last Modified: 2013-11-08
One of my computers suddenly died while in use. Basically it just lost power completely. Can't be turned on any more.  I've tried following:
1. Switch the power-on and reset power switches on motherboard hoping to see if it's power switch's problem. But reset switch does not turn computer on either.
2. Clean up the whole computer and pray problem just goes away :)  Seriously, it's been sitting on carpet for the last couple years and got a lot of dust, might cause short or component failure. Anyway didn't work.
3. Checked and made sure power strip worked (used the same power cable on another power supply and it worked).
4. Disconnected all HDs and modems, adaptors, memory, basically everything except for power switch and connectors to power unit, and still power won't come on.

However, after all these things were done, I noticed that when I push power switch, the CPU fan turns 1/8 turn and stops (I might have overlooked this before), meaning the power is on (I also accidentally shorted the power unit and burned the screwdriver).  But why is the power not enough to even drive CPU fan?  Is it power unit partial failure or motherboard problem?  What should I do before buying new power unit/motherboard/computer?

Thanks much in advance!  Will increase points for good advice.
Question by:inq123
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Assisted Solution

by:Lee W, MVP
Lee W, MVP earned 400 total points
ID: 12354387
Two things to try:

*disconnect and reconnect the power cable from the motherboard.
*Try another power supply (If you have a multimeter handy, verify the voltage coming out on one of the peripheral power connectors.

Expert Comment

ID: 12354681
You may have already done this, however, every power supply I have seen that was made in the last few years have an additional on/off switch on the back near the fan... Try turning that off then on..

Alternatively, as lew has said, try another power supply..

Accepted Solution

module7 earned 1000 total points
ID: 12354847
Your problem could be, as you suspect, a failed power supply.  However, it could also be a CPU, RAM or motherboard problem.  I agree with leew that swapping out the power supply would be a good first step.  If you don't have a spare, you could try temporarily removing one from one of your other computers.  I know that's a pain, but part swapping is THE primary tool in the computer technician's arsenal.

Since you have an ATX power supply, keep in mind that the motherboard tells the power supply to turn on.  And you mentioned that you have disconnected all memory.  Most motherboards won't boot with no RAM, and might not even switch on the power supply.  So I would definitely re-install the ram for your next tests if you have removed it.

If you swap power supplies and still doesn't work, my next suggestion would be to swap RAM.  Dead RAM is another boot-stopper.  Do your tests with one RAM module installed at a time, because often just having one bad one in the mix can mess you up.  Sometimes a RAM slot on the motherboard can go bad, so try each RAM in every slot.

One last "easy" test:  try swapping your video card.  It's rare, but a bad card can bring your system down.  You've already removed all non-essential cards, but that doesn't eliminate the video card possibility.  To be sure, swap in a different video card, preferably a PCI card in a different slot, to eliminate the possibility of a bad AGP slot.

If none of those do it, that pretty much narrows things down to the motherboard and CPU.  And if you get down to that, hey, you've been wanting to upgrade anyway, right?  So there might not be any point to trying to isolate which one is at fault, since you are likely to replace both.  Just a thought.

I hope that helps.  Good luck getting up and running again!
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Assisted Solution

kpaske earned 200 total points
ID: 12354877
It sounds like your power supply probably died on you.  That is a very common point of failure on many PC's.  If you read through answers from this week alone I think there were at least 4 or 5 other people whose power supplies needed to be replaced.  However, I'm curious about your comment "I also accidentally shorted the power unit and burned the screwdriver".  Can you explain more fully what you mean by this?

It sounds like you've covered most of the bases - clean out the computer, reseat the cables, strip down to the bare minimum (mobo, proc, ram x1, hdd x1, graphics).  If it's still not working, it is very likely the power supply.

The two suggestions above are good ones.  Test your PS with a multimeter and/or swap out for another power supply (even if you have to borrow one).  If you wind up buying a new power supply, make sure you get one of good quality (Antec and PowMax are good brands) and I suggest at least 400W or more.

The reason your fan spins for a split second is because, as you suspected, power supplies generally don't fail 100%.  There may be enough functioning components inside for a trickle of power to get through before it shuts itself down.

Expert Comment

ID: 12356411
Make sure the power supply is adequate to your needs, your machine might be drawing too much power and therefore shorting out the power supply... Find a wattage calculator and check it out.

Expert Comment

ID: 12356553
I had the same problem on a siemens pc.

Checking it, i discover a cable disconnected into the case.

Check it.

The first cable is going on the mother board from power supply.
the second cable is going on the mother board from the button used to turn on the machine.

Expert Comment

ID: 12356894
If you can borrow a PSU from a friend, try that.
If not, you can take your PC to a repair shop and ask if they can check that for you. Will save you the problems if you replace the wrong part...

Stripping to essentials, even without HD or Ram, should ad least give you access to BIOS, so fans should be spinning. If this isn't so, then the prob is mainboard or PSU, so I advise you to focus on those 2.

You can also take out the PSU and check it in another computer...

Author Comment

ID: 12358314
Thanks so much for so many quick replies! Here's what I've tried:

1. leave only one RAM on, same problem regardless of the slot/RAM chip used (I switched among two slots two chips).
2. leave only one HD, one RAM on, same (switched among two HDs).
3. Finally took the pain and pulled yet another power supply out (last night I actually tried to pull one out of an old computer but that one's not ATX and have different connectors), and put it in my computer, and yes it booted! (well, I probably should've waited till it actually booted up, but I didn't have the time this morning).

So it's the PSU again!  I increased points since it's great to have your help!

Now one last question: For my 300W ATX PSU, can I just buy any 300-500W ATX PSU online or local and it would for sure work for my AMD computer (forgot the motherboard name), or do I need to worry about compatibility?  Thanks!

Author Comment

ID: 12361015
Hello, before I award points, can anyone answer my last question:

>Now one last question: For my 300W ATX PSU, can I just buy any 300-500W ATX PSU online or local and it would for sure work for my AMD computer (forgot the motherboard name), or do I need to worry about compatibility?  Thanks!

Expert Comment

ID: 12363114
If you are buying a new power supply, any old one should work.

If you get a used one, be sure it meets at least the same version of the ATX specification as the dead one, and that it has the additional 4-pin power connector, if your motherboard requires it.

You can probably get a new inexpensive generic power supply for about $30.  The main advantage of more expensive brand-name models is that they will probably last longer.  They usually also produce cleaner power, but the cheap generics are usually adequate.  If your system was working reliably before the old power supply died, then I would say there's no need to spend more money on a higher-wattage model.  Unless of course you are contemplating adding devices or upgrading components.  Current generation video cards in particular are requiring a lot more power than the older models used to.


Author Comment

ID: 12365327
yeah, got a new 300W and it worked great, thanks for your reply!

Expert Comment

ID: 12369805
The only situations in which you have to worry, are:

- modern P4 computer (prescott, northwood, ...) - needs extra 4-pin connector
- general fast PC (P4 / AMD) with 4 or more drives & recent vid card (NVIdia, ATI): need quite some power (400W or +)

If the hardware isn't that recent, you can just buy some generic PSU. If you want to keep it arund for a while, even when you toss out the rest of the hardware, you can opt to buy some decent 400W + PSU, but that depends on your taste :)


Expert Comment

ID: 12370815
Hm, left this question open a bit too long, you already got it :p

I'm working too, going home in a few mins, so if you got any questions, just fire away :)

Author Comment

ID: 12372807
Thanks a lot Gaud!

Expert Comment

ID: 15139455
Have the same problem as stated above- have changed out the power suppy and both allow the cpu fan to come for 10 to 15 seconds before shuting down. Hve tryed both power supplies in a good computer and both work. Now what???Help

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