Fan spins on for a split sec

[csviegas]

I turned off my computer and now when I turn it on the fans only spin on for a sec and then stop (computer wont turn on). Is it a power supply problem? I tried disconnecting everything and still the same problem. Any ideas?

 

[Jonsey]

I had a dead motherboard that gave me similar symptoms.

 

[csviegas]

alright thanks. Anyone else think it could be something else?

 

[Awol]

I've seen a number of things casue this.

Assuming newly assembled, or recently worked-on system:
Floppy drive power connection one pin off. This shorts 5V or 12V to ground.
Motherboard standoff in the wrong place under a newly installed board. (Seen this more times than I can count.)
Extra power supply wire getting caught in edge of case when cover is put on. Cover is just sharp enough to pinch through insulation on 5V or 12V line, shorting power supply output.

Older system:
Bad motherboard, check for bulging caps around CPU.
Bad power supply. Disconnect EVERYTHING but AC power cord and use a paperclip to connect the green pin of ATX connector to any ground wire. (Any black wire in ATX connector, or the case of the power supply.) This will give the power supply the signal to turn on.
I've seen a shorted diode on a WD hard drive cause this. (The actual chain of events was that a power supply failed, which blew the diode on the hard dirve. A new power supply was installed, with the same symptoms. Further checking pinpointed the drive.)

Awol

 

[ICE_9]

I have left the jumper on the CMOS once to clear it and it did that same thing. Might wanna check that. Also had something where the power switch and reset switch connections were backwards once I think.

Adding information like,

1. Is this a new build, been working for a little while, well used computer?
2. Is this a OEM build or a custom build?
3. What were you doing that caused you to turn it off? (errors, sounds, or just shutting down for the night)
4. Some system specs of what you are diagnosing such as processor, board, power supply, ram, and HD.

All suggestions. Take them as you like.

 

[Elledan]

First thing you do in this case (after checking for the obvious causes, such as loose wires and bulging caps, as pointed out earlier), is taking the entire system out of the case and set up the mainboard on a piece of cardboard or similar with only the CPU installed, and a PC speaker if the mainboard doesn't have an onboard one. Connect the PSU and power the system on (front I/O-header PWR_SW pins; short for a second with something conductive). The mainboard should start beeping at you because of missing RAM, then, after you add one or more sticks of RAM, due to a missing videocard. If you hear no beeps at all, reset the CMOS, replace the CMOS battery and sacrifice a small animal.
If it still doesn't give any sign of life, try another PSU. If that fails, another CPU.

 

[spine]

I had a dead motherboard that gave me similar symptoms.

Yeah, me too. My brother had a motherboard that was DOA that did exactly as the original poster described.

 

[S1nF1xx]

You're not daisy chaining a bunch of case fans together are you? I did that once way back in the day. Tried running 4 120mm fans of one connector. There wasn't enough amperage and the fans just kind of 'ticked' if you will. Ooops.

 

[bonkrowave]

Make sure you have the CPU fain plugged into the correct 3pin header on the Mobo. My rig had the same problem, the fan would spin for just a split second then shut down. This was because the CPU fan was not plugged into the CPU.

My only other thought is that it could be the PSU.

 

[Milenko]

I've seen a number of things casue this.

Assuming newly assembled, or recently worked-on system:
Floppy drive power connection one pin off. This shorts 5V or 12V to ground.
Motherboard standoff in the wrong place under a newly installed board. (Seen this more times than I can count.)
Extra power supply wire getting caught in edge of case when cover is put on. Cover is just sharp enough to pinch through insulation on 5V or 12V line, shorting power supply output.

Older system:
Bad motherboard, check for bulging caps around CPU.
Bad power supply. Disconnect EVERYTHING but AC power cord and use a paperclip to connect the green pin of ATX connector to any ground wire. (Any black wire in ATX connector, or the case of the power supply.) This will give the power supply the signal to turn on.
I've seen a shorted diode on a WD hard drive cause this. (The actual chain of events was that a power supply failed, which blew the diode on the hard dirve. A new power supply was installed, with the same symptoms. Further checking pinpointed the drive.)

Awol

Had the same problem here. Dead HDD would not let the machine even turn on.

 

[Awol]

Had the same problem here. Dead HDD would not let the machine even turn on.

On more than one occasion, I've desoldered the affected diode and got the drive up and working. (WD's in the 3 - 10GB range, IIRC)

The diode was designed to protect against reversed power input and bad power supplies. Whether it was designed to or not, it acted as a sacrificial component, protecting the rest of the drive from the "bad" power. Removing the diode leaves the drive with no future protection against another catastrophic power event, but did get the drive up and working. Better than -not- having the drive at all.

 

[Ignad]

-clear cmos
-Check for electical shorts (as explained above) and check all cabling for proper seating.
-Disconnect non-essential hardware (floppy, cd-rom, sound card, nic, modem, etc)
-Swap essential hardware one piece at a time (inspect em for visible damage, smell em too!) till you find the culprit


Offhand, I have seen:
AGP video card not seated 100% correctly in slot (AGP can be VERY sensitive!)
ram not seated correctly, shorting out.
motherboard standoff in wrong place
cables shorting on sheet metal edge
too much load on power supply
bad cmos settings
bad motherboard
bad cpu
bad power supply
bad attitude

as causes

good luck

 

[pigwalk]

Assuming newly assembled, or recently worked-on system:[/I]
Floppy drive power connection one pin off. This shorts 5V or 12V to ground.

How can you check this and fix it? I have a psu that shorts whenever I use the floppy connectors and I'm guessing this is it. Could this cause the PSU to run hotter than it needs to?

-wil