Computer will not power up properly

[Tels]

I'm fixing a computer for my dear mum. It's an ATX (intelligent power) board running a celeron cpu with 512 MB memory.
The problem is it's refusal to power up, or rather, the 'soft' power button does switch on the power supply, but there's nothing on the screen and all peripherals remain dead. (no power to the hard drives, cd-drives etc)
I have tried 3 different power supplies, (all known to work) and the same problem.
I've seen a similar problem, when the CPU clock speed is not configured correctly, but I'm fairly certain this would not cut off power to the peripherals.
I have to say I'm currently in the process of checking clock speeds, but the celeron is known to be easily over-clockable, so I think I shuld have had a response by now, I'd like to know if anyone else has had the same problem, and what the fix was, before I write off either the m'board, or the CPU.
Also is it normal for an ATX board to be able to isolate and control power to the peripherals only?, and under which circumstances it should do this, (like a sleep mode perhaps)

Heres hoping someone has a clue.......

Cheers
Tels

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[Tels]

to recap:
the board senses when the power button is pressed - it ain't totally dead

but

all it does is switch on the power supply. and the cpu fan.

ps. the power button won't switch the computer off again - so it appears to ignore the power switch once it is on, and the only way to switch off is to pull the plug.

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[ErikZ]

Well, if the fan is working, that rules out a short in the system. Isn't the fan powered from the power supply?

Ideally, you could get your hands on another motherboard and boot it up, or bring your motherboard to someone elses case and plug it in and see if it works.

 

[Tels]

I'll try both tonight, but the same problems remain, namely is it the CPU or the board? the problem is I just fixed a mates computer with the same chipset, so I have the stuff to replace bits and test it all out, but if I swop the CPU's around to test them I might still miss the mark completely, and I don't want to naff both computers up after I just fixed the other one....

The point is I can't be sure whether it's the board or the CPU.

Cheers ErikZ- keep it coming.
Thanks
Tels
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[bosully]

I'm curious, how did the problem start to manifest itself?

I have a Celeron PC (on a micro ATX) that recently gave me big trouble. Problems started with program freezes and spontaeneous reboots while running memory intensive software. This continued until the system was virtually like yours, ie only the CPU fan would come on when booting.

After a few weeks in a repair shop where the "technicians" surmised that either the processor or motherboard had been damaged by a power surge, I managed to fix the problem myself. Apparently, the CPU fan had begun to creep out of position and wasn't blowing directly on the processor. This in turn was leading to problems with over-heating!

I know it sounds stupid and may be an unlikely answer but that's what I would have said four weeks ago.

Brendan

 

[stuartd]

I have the same problem, but this was since my PSU blew up!!
I haven't got to the bottom of my problem yet - I am currently removing all components and starting as if it was a new project.

 

[Tels]

Hmmmm Yes. apparently, my dear mom just switched on the PC and it didn't work, seems the PSU blew up, however the board is usually protected isnt it? as the voltage running to it is quite low.... like I said, the only real way to check would be to switch the CPU's around, but one is sealed to the fan, the other is covered in arctic silver, and I have no way of divining the CPU speeds! neither of the boards is capable of auto sensing the speed, so its a bit of pot luck to find the right settings and I can't take the risk of damaging my friends CPU..... oh dear...

Well, I'll try all your suggestions out, could be a malfunction or a hot core... one thing though, are you sure all your peripherals died as well? at the moment I can't even get the CDRom to open or anything...

Thanks for your help...... if it leads somewhere I'll pile on the stars!!

Tels
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[ceh4702]

Try it with just a floppy, the memory, and a video card, and the CPU/fan.

It could also be just the memory. Memory sometimes goes bad.

If it works add one device at a time.

This could be a good opportunity to upgrade to a new motherboard. If you do not like my post feel free to point out your opinion or my errors.

 

[ErikZ]

I've only had a bad memory chip once, but the computer still booted. It was a laptop and the BIOS was set to skip the memory test when I bought it.

Even if you have no memory in the board, I would think that it would give error beeps. But then again, I could be wrong.

 

[Laffalot]

Hi,

Some power supplies employ a power supply health signal before fully powering up. Does your motherboard supply this.

When you switch on do you get any beeps. If not then the processor is not even carrying out a POST test. So big time failure. Either the motherboard or CPU. Takes yer pick at which to swap first. The CPU is the easiest, but what if its then motherboard and that damages the CPU ?. Its a catch 22, take a chance or bin them both and treat your mum to a brand spanky new machine. Shes your Mum.

As for the switching off, try holding in the power switch for 5 - 10 seconds and see if it powers down (usually set in the bios to prevent accidental power down - not that you can check this seeing as your mums machine is dead)

regards

 

[Tels]

Well done. you said the same thing as I would have said.

nope, nothing, nada. no POST beeps, no display, nothing. the board senses a power switch on but won't take a switch off. the only visible signs of life at all are the PSU and CPU fans switching on, and the power LED. no memory clicks, no HDD whirr, nothing. it's a big expensive air-blower.

(saying that the video card processor heats up, I felt the heat coming from it - proves that the board is powering the video card but I hope it isn't damaging the video card)

I've little doubt either the CPU or board is blown, but I was hoping someone has already had this kind of problem would know if there would be different symptoms when the CPU blows as opposed to the board?

I reckon it is marginally more likely to be the CPU. At least the board 'powers up'

I'm gonna take the CPU out of another PC and switch it on (minus CPU) to compare symptoms............. good idea or not you think?

No matter what I still think it's wierd that the peripherals are starved of power, ie HDD CDROM FDD etc, but the power supply is definately rated for that board.

A little birdie tells me the PSU was found to be blown after someone else tinkered with it (not me) but whether that was already there or happened as a result of their skill, I don't know.

Cheers to all the guys n gals who tried to help - you're great
I'll let you know what happens

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