pc turns off immediately after turning on

I have a pc with a gigabyte motherboard which has been working ok for
the last 2 years.

Two days ago, it turned off on its own. Since then, when I press the on
switch, it briefly comes on for about 1 second and goes off (lights and
fans come on and go off after 1 second).

What could be wrong? Faulty switch? Power supply finished?
Motherboard/CPU faulty?

"Nick" wrote in message
oups.com...
I have a pc with a gigabyte motherboard which has been working ok for
the last 2 years.

Two days ago, it turned off on its own. Since then, when I press the on
switch, it briefly comes on for about 1 second and goes off (lights and
fans come on and go off after 1 second).

What could be wrong? Faulty switch? Power supply finished?
Motherboard/CPU faulty?

Could be any of those things. However it could just be that the CPU fan is
u/s. Although it may still be going round, if the speed sensor has stopped
working, your mobo will see the fan as not working and shut the system down
in the manner you describe. So, as they are cheap, try another fan on the
CPU heatsink and see what happens.

SteveH

In article , "SteveH"
wrote:

"Nick" wrote in message
oups.com...
I have a pc with a gigabyte motherboard which has been working ok for
the last 2 years.

Two days ago, it turned off on its own. Since then, when I press the on
switch, it briefly comes on for about 1 second and goes off (lights and
fans come on and go off after 1 second).

What could be wrong? Faulty switch? Power supply finished?
Motherboard/CPU faulty?

Could be any of those things. However it could just be that the CPU fan is
u/s. Although it may still be going round, if the speed sensor has stopped
working, your mobo will see the fan as not working and shut the system down
in the manner you describe. So, as they are cheap, try another fan on the
CPU heatsink and see what happens.

SteveH

The BIOS has that fan checking feature in it, on some
motherboards. It might take several seconds for the BIOS
to figure that out, that the fan is too slow.

The Athlon64 and Pentium4 have THERMTRIP, which is an internal
detection of overheat. That signal is connected into the PS_ON#
signal logic that controls the ATX power supply. If the heatsink
falls off your processor, then shutdown in 1 second would be
about right. If the fan is stopped, it might take a bit longer
before the silicon die can heat up the heatsink enough to
trip the overheat detection.

The Athlon(32) didn't have thermal protection built into the
silicon die. But some versions did have a thermal diode, suitable
for monitoring with an external device. Some motherboards, like
the A7N8X series, had a small eight pin chip, that checked the
thermal diode output, and prevented burnout. Some other Athlon
motherboards used their hardware monitor chip to measure
the temperature, but there was no guarantee that the processor
would realize it was overheating in time. And lastly, there
were some other moherboards, that had no protection implemented
at all.

The power supply probably has its own protection logic, and
the complexity of that logic (what it is checking for) depends
on the price of the supply. Overvoltage, undervoltage, overcurrent
are some possibilities, and even internal PSU temps might be
another reason to shutdown.

If the motherboard was faulty, it might just stay off or
stay on. Turning on for a second and then turning off, is
a little too clever for a motherboard on its own :-) While
I can think of ways it might happen, I've never read of any
such cases.

I would check the condition of the heatsink/fan on the CPU
very carefully. Including, as SteveH has pointed out, that
the fan is still plugged in, and spins when the machine tries
to start. If the fan spins, but the machine still shuts down,
check the heatsink to see whether the clips are still
applying enough pressure to keep the heatsink in contact
with the processor. Sometimes a tab will snap and a clip
will come loose.

And if there is no effective thermal interface material between
the heatsink and the CPU, like you used a thermal paste that
dried out or pumped itself out from between the heatsink
and CPU, that would be another reason for the CPU to overheat.
The material that ships with an AMD or Intel processor, is
not likely to do that, while a hobbyist applied paste is
more likely to leave the scene on you.

Paul

"Paul" wrote in message
...
In article , "SteveH"
wrote:

"Nick" wrote in message
oups.com...
I have a pc with a gigabyte motherboard which has been working ok for
the last 2 years.

Two days ago, it turned off on its own. Since then, when I press the on
switch, it briefly comes on for about 1 second and goes off (lights and
fans come on and go off after 1 second).

What could be wrong? Faulty switch? Power supply finished?
Motherboard/CPU faulty?

Could be any of those things. However it could just be that the CPU fan
is
u/s. Although it may still be going round, if the speed sensor has
stopped
working, your mobo will see the fan as not working and shut the system
down
in the manner you describe. So, as they are cheap, try another fan on the
CPU heatsink and see what happens.

SteveH

The BIOS has that fan checking feature in it, on some
motherboards. It might take several seconds for the BIOS
to figure that out, that the fan is too slow.

The Athlon64 and Pentium4 have THERMTRIP, which is an internal
detection of overheat. That signal is connected into the PS_ON#
signal logic that controls the ATX power supply. If the heatsink
falls off your processor, then shutdown in 1 second would be
about right. If the fan is stopped, it might take a bit longer
before the silicon die can heat up the heatsink enough to
trip the overheat detection.

The Athlon(32) didn't have thermal protection built into the
silicon die. But some versions did have a thermal diode, suitable
for monitoring with an external device. Some motherboards, like
the A7N8X series, had a small eight pin chip, that checked the
thermal diode output, and prevented burnout. Some other Athlon
motherboards used their hardware monitor chip to measure
the temperature, but there was no guarantee that the processor
would realize it was overheating in time. And lastly, there
were some other moherboards, that had no protection implemented
at all.

The power supply probably has its own protection logic, and
the complexity of that logic (what it is checking for) depends
on the price of the supply. Overvoltage, undervoltage, overcurrent
are some possibilities, and even internal PSU temps might be
another reason to shutdown.

If the motherboard was faulty, it might just stay off or
stay on. Turning on for a second and then turning off, is
a little too clever for a motherboard on its own :-)

Not at all, this is exactly what happens when the CPU fan speed sensor isn't
being read for some reason.

While
I can think of ways it might happen, I've never read of any
such cases.

I would check the condition of the heatsink/fan on the CPU
very carefully. Including, as SteveH has pointed out, that
the fan is still plugged in, and spins when the machine tries
to start. If the fan spins, but the machine still shuts down,
check the heatsink to see whether the clips are still
applying enough pressure to keep the heatsink in contact
with the processor. Sometimes a tab will snap and a clip
will come loose.

Except I didn't say that. I pointed out that if the speed sensor on the CPU
fan fails, then most BIOS will stop the system to prevent CPU overheat. This
is something I've seen and fixed by the simple expedient of replacing the
fan several times. I've also seen this happen where a person building a PC
has accidentally plugged the CPU fan into the wrong header.

SteveH

Just tried a few things one of which gives a clue.

If I unplug the ATX12v power voltage (I think this goes to the cpu) and
then switch on, the power and fans stay on although the pc does not
boot up for obvious reasons.

So it could be something to do with the cpu (heatsink, fan, power
supply, processor)?

"Nick" wrote in message
ups.com...
Just tried a few things one of which gives a clue.

If I unplug the ATX12v power voltage (I think this goes to the cpu) and
then switch on, the power and fans stay on although the pc does not
boot up for obvious reasons.

So it could be something to do with the cpu (heatsink, fan, power
supply, processor)?

It could still be the CPU fan. If you have another fan avialable (it can be
a case fan, if it has the right connector), plug it into where the CPU fan
plugs into the mobo, and then try switching on. If it stays on, it means I'm
right and your CPU fan needs replacing.
If it does indeed stay on, tap the delete key (or whatever you need to do to
get into your BIOS and then switch off again (you may have to hold in the
power switch for 4 secs). Go and get yourself a new CPU fan and fit it, job
done!
If the above doesn't work, then you will need to start investigating other
possibilities. The above could be the cheapest fix however.

SteveH

Most likely the PSU has failed. If not, then the motherboard would be the
second most likely culprit.

--
DaveW

----------------
"Nick" wrote in message
oups.com...
I have a pc with a gigabyte motherboard which has been working ok for
the last 2 years.

Two days ago, it turned off on its own. Since then, when I press the on
switch, it briefly comes on for about 1 second and goes off (lights and
fans come on and go off after 1 second).

What could be wrong? Faulty switch? Power supply finished?
Motherboard/CPU faulty?

"DaveW" wrote in message
...
Most likely the PSU has failed. If not, then the motherboard would be the
second most likely culprit.

--
DaveW

In my experience, the most likely culprit is the speed sensor in the CPU
fan, the failure of which often causes the symptoms the o/p describes. But
as you say, could be the mobo, PSU etc.

SteveH

I just borrowed a cpu fan off another pc and tried it and there is no
difference. So its not cpu fan.

I am going to replace the power supply next. Watch this space.

"Nick" wrote in message
oups.com...
I just borrowed a cpu fan off another pc and tried it and there is no
difference. So its not cpu fan.

I am going to replace the power supply next. Watch this space.


Is the 4-pin power connector from the power supply attach properly
to the motherboard?


---
Kevin Chalker, Owner (KC COMPUTERS)
E-mail: Web: www.kc-computers.com
Internet dealer since 1991!!! See WWW.RESELLERRATINGS.COM!!!