CPU Fan stops few seconds after starting PC - most components have been replaced

Posted on 2008-06-18
Last Modified: 2013-12-11
I've seen similar posts with this issue, but none of the suggestions have helped me resolve the problem.


I had a home-built PC until one day when the CPU overheated and the whole system refused to boot. I checked the CPU and it looked fine, so I salvaged an old Motherboard from my brother's PC (he upgraded). The system wouldn't boot, but the CPU fan and one case fan would spin for a couple of seconds. So I replaced the CPU with an older P4 (went from potentially fried P4 2.4GHz to P4 2.0GHz). Same problem. Thought it might be the Power Supply, so I bought a new one (550W Thermaltake, 200W larger than orginal PSU). Same problem. Replaced CMOS battery. Still same problem. I've upplugged all components save the video card (ATi Radeon9700), and I still have the same problem: CPU fan spins (if pugged in) for a couple seconds and monitor goes from standby to awake to standby. The CPU heat sink is correctly installed/seated using Arctic Silver, and the room is cool. I have 3 DIMMS of 512MB RAM that I've swapped out and tried.

My next step is to try the boot without the video card, but I don't think it's the problem.

Any ideas?!?

Question by:josanbabu
LVL 10

Expert Comment

ID: 21818350
Double check to make sure that you have any extra power connectors to the mobo connected, specifically the 4 pin square 12v connector, in addition to the usual 20/24 pin main connector.  I'd also try to boot without the menory and the video card to see what happens, see if you get some beeps at least.
LVL 91

Expert Comment

ID: 21820346
it maybe a bad motherboard, since it does not boot with different cpu's
check also the caps  :

Author Comment

ID: 21824131
My next step is to attempt a boot with an empty case - motherboard, cpu, and power supply only (no memory DIMMS, fans, heat sink, video card, drive, or other peripheral). If that passes, I'll start adding things one by one.

I had check the capacitors on the mobo previously, and they look OK. Only one of them is ever so slightly convex, but the rest have a healthy concave shape. Could one capacitor be the source of the issue? The mobo I'm using was perfectly fine before it was harvested from another homemade PC.

LVL 91

Expert Comment

ID: 21828866
>>  My next step is to attempt a boot with an empty case - motherboard, cpu, and power supply only (no memory DIMMS, fans, heat sink, video card, drive, or other peripheral).    <<<    NO ! NO !

you need the cpu fan cooled and the fan running  at all times !
you cannot boot without Ram - it will only beep at you - 1 stick is needed
>>  Could one capacitor be the source of the issue?   <<   it can be, and the visual inspection only reveals the very obvious bad ones, it does NOT guarantee they are ok. The only test is with another mobo

Expert Comment

ID: 21831669
This is a fun one since it could be a bad board, cpu, memory, or PSU.

Typically you will get some beeps if there is a bad component though so I would try with a different PSU if you have one laying around.
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Expert Comment

ID: 21892514
> CPU fan spins (if pugged in) for a couple seconds

Have you tried replacing the fan? I've seen bad fans give a similar symptom - fan works for a little while then stops. Or I help the fan get going and then is stops after a little while.

Another thought is that on some motherboards there are hardware monitor chips that check and regulate temperature. There are utilities that can manipulate this.

Author Comment

ID: 21892694
Sorry for the delay. Attached is a status update:

I tried booting the PC in bare bones mode -- PSU, CPU, and Mobo only -- to see if I could at least far enough in the boot process that I'd hear the "hey, you don't have any memory DIMMS installed" beeps. But alas, it stops well short of that point. So...

I doubt it's the PSU, since I bought a new one and both the new and the old exhibit the same symptoms. So it's either the mobo or the CPU, as originally guessed. But I'm surprised that either BOTH mobos (my old mobo and the old one that my brother sent me) or BOTH CPUs (my old CPU that overheated and my brother's P4 that he sent me (he upgraded to a dual core a few months ago)). It just seems very unlikely that both mobos or both cpus would fail AND would have the same symptoms.

Upgrading becomes problematic as well because I have older IDE HDDs and most new mobos are geared for SATA. And since my problem could lie with either the mobo OR the CPU, I could end up buying both (mobo first, then CPU if that fails), and it might just be cheaper to buy a new PC (rather than going the homemade route again).

Any sage advice?
LVL 39

Accepted Solution

PUNKY earned 250 total points
ID: 21892704
You can buy an IDE PCI card as in the link:

Many good motherboard can be found here:

Motherboard with old P4 cpu can be found here:

You should invest one time for motherboard and CPU that is better.

LVL 91

Expert Comment

ID: 21893166
>>  PSU, CPU, and Mobo only    <<   i told you you need 1 Ram stick !

Author Comment

ID: 21898727
nobus - I attempted to boot without a RAM stick to see if it would beep at me. It did not, so I assume it didn't make it that far in the boot process.

Punky - I'll probably buy an IDE mobo, but if that doesn't work, I think I'll put the money toward a new PC rather than a P4 CPU.

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