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PC powers up for a few seconds / minutes, but doesn't boot

Discussion in 'Motherboards' started by pike_by_nature, Jun 11, 2007.

  1. I suspect I already know what my problem is - but can anyone advise me
    on how to prove it?

    I often have to boot my PC up two or three times for it to boot
    properly. Usually, the red "hard disk" light comes on and stays on at
    boot up, and nothing else happens. I reboot once or twice, and it's as
    good as gold.

    Yesterday, the PC wouldn't boot. The monitor just remains blank. No
    ram counting, no "press delete to enter bios", no beeps, nothing. The
    fans come on, including the CPU fan and after a few seconds, it
    switches off. I switch it back on, and after a few minutes, it
    switches off. Still nothing. I've removed every peripheral going,
    taken out the ram (one chip at a time), removed and replaced the CPU
    (P4 2.8). The CR2-32 battery is less than 12 months old - I replaced
    it last year suspecting it might be responsible for my boot-up

    The motherboard is a Gigabyte GA-8IPE1000; so it's about three years
    old. I suspect it's lost the bios somehow. Can anyone offer any


    pike_by_nature, Jun 11, 2007
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  2. pike_by_nature

    Paul Guest

    What shape is the power supply in ? Maybe the power supply is switching
    itself off. Maybe it isn't delivering the PWR_OK signal when it powers up.
    Power supply failures are a common enough fault, that you could start
    by swapping in a spare. Using a multimeter may tell you something, but
    if it shuts off before you can examine all the pins on the main
    connector, you may not get a complete picture.

    You can contact the metal pins, while the connector is plugged into the
    motherboard (from the back, where the wire enters the hole for each
    pin). Pinout for 20 and 24 pins supplies can be found in these
    specs. Using an alligator clip, and connecting the (-) lead to
    an I/O connector screw, makes it easier to probe the machine with
    the (+) lead, using one hand.


    If you don't own a multimeter, and don't want to check anything, just
    try another power supply.

    In the description, I don't see how the BIOS is responsible. If the
    thing eventually boots, then there must have been BIOS code, and
    it must have been spotless, to pass the checksum test early in the
    POST sequence.

    If this was purely a motherboard failure, about the only reason
    for the motherboard deciding to turn things off, is if the CPU
    overheated. Otherwise, if the processor doesn't boot or doesn't
    appear to execute code, there is precious little reason for the
    power to go off. So something has to help it. A bad power supply
    can switch itself off if it wants. Software also knows how to
    turn off a machine, but it has to run to work. Safety features,
    like THERMTRIP (that is the CPU overheat protection) can do it.
    But you've already been playing with the CPU, applied fresh
    thermal paste, checked the clip, that the fan runs, and so on,
    so it probably isn't overheat. I'd try another power supply.

    Paul, Jun 11, 2007
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  3. Thanks Paul - yesterday, it wasn't booting at all. I never got as far
    as the Bios screen - that's what makes me wonder if the BIOS is
    responsible. I know that it's incredibly rare; and you're probably a
    lot closer with your thought re the power supply; I'll give that a go
    when I get home this evening - I've got a couple of spares laying
    around - and see what happens.

    Thanks again;

    pike_by_nature, Jun 11, 2007
  4. pike_by_nature

    Wes Newell Guest

    Might want to also check the caps on the MB for bulging and leaking. If
    your bios checks the fans, it's also possible there's a problem with a fan
    speed being read properly. Bad video cards would also present this type
    Wes Newell, Jun 11, 2007
  5. Hi Paul, Wes;

    Changed the power supply - made no difference. I removed all the
    peripherals; video card, ram and in the end, even the CPU; there is
    now nothing attached to my motherboard but a power supply (and I've
    done it with both), and it just powers up for a couple of seconds, and
    powers down again. Very irritating.

    Not sure what Wes meant by the "caps" on the motherboard - but there's
    no obvious signs of burning or melting.

    pike_by_nature, Jun 12, 2007
  6. pike_by_nature

    Paul Guest

    Would the power switch be sticking in the "ON" state ?

    Try connecting the reset switch to the two pins intended
    for the power switch. That will allow you to use the
    reset switch as a fake power switch, just for testing.
    If it stays powered up, you could have a bad computer
    case switch.

    Wes is referring to electrolytic capacitors. They are the
    aluminum cylinders with the plastic sleeves on them. Normally
    the top of the cylinder is flat. If pressure builds up inside
    them, the top bulges, and the pressure relief lines break.
    Alternately, electrolyte leaks out the bottom of the capacitor,
    and leaves a brown stain on the motherboard.


    When that happens, extra load is placed on the Vcore regulator
    switching circuits. Some of them are equipped with overcurrent
    detection. But I don't know if the symptoms in that case would
    include shutting off the PC or not. From a hardware point of
    view, it doesn't have to. The Vcore regulator chip can simply
    shut itself off, and eventually the user will notice.

    A visual inspection of the capacitors, will give you some idea
    if this is a problem or not.

    Paul, Jun 12, 2007
  7. Thanks Paul; I'll give it a go; but although last night it was
    starting and dieing after 4 - 5 seconds, the day before, it was
    starting, and going for 30 seconds to two minutes; without any boot
    sequence or anything; just the lights on, fans whirring; nothing else,
    and then shutting down. So while it's definitely worth a go, I suspect
    the switch will prove to be okay.

    (I'm coming round to the "it's trashed" theory again!)

    pike_by_nature, Jun 12, 2007
  8. pike_by_nature

    Wes Newell Guest

    Paul explained the caps. The system won't boot without a cpu. So that
    really doesn't test much, if anything. You have to have MB/CPU/ram/video
    card to see anything of value. If you are never getting any video, then
    connect the case speaker and see if you are getting any beeps. Different
    beeps mean different things. If you're getting beeps, that will tell you
    Wes Newell, Jun 12, 2007
  9. Well, no bulging caps. I also swapped out the power and reset switches
    - the fans come on, but nothing else (well, until they go off again,
    which seems to be a variable time between 2 seconds and one minute -
    very approximately). The internal speaker is connected, but I don't
    get any beeps. The boot up sequence never even starts. The PC just
    wakes up, but nothing else happens at all. I've now put back the CPU,
    RAM, video card and hard disk - but I still don't get anywhere at

    Methinks I might get a quote from my local parts supplier for a P4
    motherboard that will take my DDR 184 pin ram!

    pike_by_nature, Jun 13, 2007
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