PC no power

  Simon2 15:55 15 Apr 2008

Hi all

I've got an ASROCK P4VM800 mobo that was working fine until one night I heard some clicky noise & it switched itself off with no avail to power it up again.

A new more powerfull PSU installed but still no power up.

Just to clear few facts:-
Case switch works fine.
PSU works by jumping the green & black wires.
Went through all steps in the following thread:-

click here

But I noticed that by leaving the 20 pin mobo power cable connected & removing the 4pin CPU power cable the case comes to life and all the fans, HDDs & CPU fan work but no screen output.
Tried removing the PCI Nvidia card & using the built in video output but the same.

What could possibly be the fault here?
Motherboard or CPU?

Whats the effect of connecting/disconnecting the 4pin CPU power cable?

Why is every thing working on removing this cable.

I need your help guys as on what to do next??


  User-312386 16:29 15 Apr 2008

Just looked at this thread

The effect of disconnecting the 4 pin is power to CPU, however, i assume your new PSU came with a 20/24 pin main PSU line? Does your mobo have 20 pins or 24?

  Simon2 16:59 15 Apr 2008

Thanks for the reply

my mobo is connected to the PSU through a 20 pin connector.

(The PSU came with a 4 pin 12v CPU power cable & a 20+4 main PSU line)
where you can split the extra 4 pins and connect only the remaining 20 pins.

  woodchip 17:56 15 Apr 2008

Dead Hard Drive. And can stop PC booting. I had one.

Try removing cables from Hard Drive to see if it goes to BIOS

  Jim_F 18:02 15 Apr 2008

Looks like either the processor or mobo is putting something like a full short across the 12 rails. You could try with the CPU out but 'clicking noise' sounds like an electrical short so a check for mountings that might have nicked a track on the PCB - sometimes the laquer gives a false but temporary sense of security.

  Simon2 18:02 15 Apr 2008


Done that already, stripped mobo from all connections (IDE,SATA & Floppy) and tried all possible combinations, nothing changes.

Besides, if it was a dead HDD, there should be some power to the mobo or something on the screen at least or a fan working to say the least.

Thanks for the suggestion but I suspect CPU or mobo but don't know how to tell.

  Simon2 18:05 15 Apr 2008


Thanks for the reply

Thats what I thought as well but didn't know what to do next.

Any suggestions on what to look for or what to do?

  woodchip 18:08 15 Apr 2008

If "mobo" the Power button will not turn comp power off if pressed and held in.

Click I would still be thinking of something that moves as it was working. what about ram. if you have two sticks try with one. AS bad ram can corrupt Hard Drive, then it would not be able to read it hence clicking

  woodchip 18:09 15 Apr 2008

Also fan may be blown if it does not turn this would make the computer shut down

  woodchip 18:10 15 Apr 2008

You can test a Fan on a Car battery

  Simon2 18:23 15 Apr 2008

[by mobo I mean motherboard]
Tested different combinations of RAM sticks, both working fine.

As I said earlier, removing the 4pin 12v CPU power cable turns the mobo on as normal but nothing on the screen.

As soon as I put the 4pn 12v cable back, no responce at all from mobo (apart from a short spin from CPU fan for 1 second and all stop) as if there was a short or fuse cutting off the power supply.

Question is how to tell wich one is faulty?
CPU or motherboard?

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