power supply, motherboard or cpu?

By ayenilmez ·
hi all,

my desktop pc doesnt start. when I turn it on, cpu fan starts reving (possibly at highest) and that's all. nothing else happens, no bios screen or error message/sound.

- removed the ram module and it doesnt even beep on startup (normally it does)
- power button turns the system on but doesn't turn it off. pressing 5 or more seconds doesn't work either. i have to unplug from the mains.
- tried unplugging all components (hdd, optical drive and ram, still unplugged).
- removed bios battery for a bit and put it back on. those didn't help.
- cpu fan speed doesn't change, it is constantly at it's highest.
- when i plug the pc to mains first time (before pressing the power button), cpu fan starts spinning and shortly after it stops. doesnt start until i press the power button.
- when pressed to power button, led that is near power button, flashes slowy and regulary (like 1s on, 1s off).

according to these findings, what do you think causing the problem? I believe it has to be either power supply, cpu or mb.

please help me to identify the problem and resolve it.


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Im getting an identical mb

by ayenilmez In reply to Well if you had of mentio ...

Col, first of all I must thank you for your detailed reply (replies, actuall).

sorry, I didnt think water damage was still in question as it did work before. but like you said in the other post, sometimes it can take some time for faults to show up.

now, in the ligth of your suggestions, Ive ordered an identical mb from ebay, which is exactly the same. so hopefully, this should sort the problems out.

for cpu (which is P4 3.2ghz, 775), I removed it and I couldn't see any visible defect, oxidation etc. So it looks all good. in fact motherboard looks fine too, but not always everything is visible.

so fingers crossed, it will work fine when I replace the mb.

thanks again for your time.

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Just be careful fitting the CPU

by OH Smeg In reply to Im getting an identical m ...

I have seen a couple of cases where some people have fitted them incorrectly and they can sit off the Contacts inside the socket or worse actually bend a couple of contacts and Render the M'Board unusable.

With the 775 Sockets there are 2 notches in the CPU that fit into raised lugs in the socket so just make sure that the CPU is correctly orientated in the socket before locking it in place.

Other than that it's a straight Swap with no real issues.

Lets know how you get on.


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still the same (almost)

by ayenilmez In reply to Just be careful fitting t ...

okay, changed the motherboard and the bad news is it is still the same, not even posting.

only difference is now power on/off is responding to shutdown (when pressed 5s or so). previously it only turned the pc on but didn't respond to anything else. I had to pull the plug. one other thing I realised is the led ligth next to power button is not flushing, it is constantly on (it did flash slowly and constantly with the other mb).

now, only thing that is left is the cpu, although there was nothing visibly wrong with it..

only other thing i can try is to buy a cpu and see if it helps. i cant think of anything else.

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Well disconnect everything but the PS and CPU

by OH Smeg In reply to still the same (almost)

Then apply power. If it starts beeping shut down and insert 1 RAM Module and try again.

Could be that you have the IDE Lead the wrong way round when you connected it to the M'Board that could cause this to happen.


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there is no posting

by ayenilmez In reply to Well disconnect everythin ...

Ive tried that but it mb doesnt post. No beep at all, with no ram, no nothing connected.

There are two main power cables connected to mainboard, I guess one for the cpu (small one) one for everything else (big one). I tried unpluging the small one but again nothing changed. I will be so happy if I could get to the "beep" stage.

back to the beggining, why would the fan on CPU would rev like crazy? It must be on its highest. Normally, this fan used go up a high speed for a second or so when pc turned on, then go back to slower rate. So that fan being on constantly high rate, would this mean that cpu is messed up or giving wrong temperature reading so that fun is trying to cool it down, and motherboard is not even going to next stage because cpu is overheated?

Im just trying to understand, this might be a really silly scenario:)

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OK well start fresh here

by OH Smeg In reply to power supply, motherboard ...

The Second Plug tot he M'Board is a Supplementary 12 V DC Plug this can be either a 4, 6 or 8 Pin Plug depending on the M'Board.

The Main Plug which has all of the voltages present for the different sections of the M'Board is either a 20 or 24 pin Plug depending on the M'Board.

Here try lifting the CPU out of the Socket and make sure that there are no bent pins in the socket. Also check to make sure that the CPU is correctly orientated in the socket. It's easy to make a mistake here.

Unlock the Heatsink's 4 Supports by turning them 90 Degrees counter-clockwise and then pull up on the Black top with the Screw Gate in it. After you have released all 4 of these supports/Locks you can lift the Heat Sink/Fan Unit off the M'Board. Unlock the CPU Socket Locking lever and lift up, when that is fully open lift the Metal Locking Plate over the CPU and then lift the CPU out.

If there are any bent pins in the Socket you'll see these very easily and the bad news is that the M'Board is toast I have one here that the person who bought it fitted the CPU incorrectly to or maybe used the wrong CPU and trashed a new M'Board. Wasn't friendly at all when he returned it I might add.

Anyway if the CPU was in properly and the Socket is OK them your sort of stuffed and have to replace the CPU though you could try cleaning the contacts on it with a soft rubber/eraser Very Gently, and refitting before ordering another CPU.

Here I'm assuming that you are using the new PS are you?

Edited to add If you have to get a new CPU make sure that the one you buy is supported by the replacement M'Board. Just because they are a Socket 775 CPU doesn't mean that the M'Board will support that CPU.


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will check for bent pins

by ayenilmez In reply to OK well start fresh here

when I go home I will check for bent pins, although when I changed the mb I didnt see any abvious sign of damage.

Yes, I did pay attention to the orientation of the cpu while replacing the mb.

I actually tried both PS, which didn't make any difference.

My mb has got one 4 pin and one 24 pin plugs.

I also tried starting the comp without cpu fan unplugged (I know this could potentially toast cpu) for a few seconds, to rule out if the fan was faulty. no success. It wont beep.

Ive ordered one cpu, now, which I think should be ok. On the hp compaq's website they dont give detailed info about motherboard but one of the cpu's listed is:
P4 640 3.20 2 MB L2 cache 800 MHz HT

and the one I ordered is:
P4 3.2 1Mb 800 FSB PC HT SL7PW

the only difference is cache, which Im hoping this wouldnt be an issue (both 775).


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