PC switches off on first boot. CMOS battery ?

October 16, 2009 at 09:03:27
Specs: Windows XP
Dear Techies,

I wonder if anyone has any clues to this odd behaviour?

A couple of weeks ago, my trusty 7 year old PC began
to spontaneously switch off while booting...usually after
POST but before Windows started. No messages, just
gone...as if I had removed power. This happened
every first boot for days on end...but on second boot,
it was fine. It didn't matter whether the first boot was
morning or evening, but the second boot would load
and stay on as long as I wanted it to.

Hmmm, thinks I...it's as if something is a bit dead, but
recharges itself by the second boot...after power has
been sent at it a while.
So...I implicated the MOBO CMOS battery!

So I changed the battery for a brand new 10 year
Panasonic...and re-entered all the now lost BIOS settings,
which I had thankfully written down...and all was well...
...for a week...

I am now getting the same symptom. First boot shuts
down and second boot is fine...but BIOS is still intact.

I guess the battery could be duff, but I wonder if
there might be anything that has drained it or if it
is a different problem entirely...which would be odd
as a battery change fixed it initially.

Any sensible and informed thoughts on this?

For what it's worth, the MOBO is a SOYO KT333.
BIOS is Pheonix Award k7vxb, which has not been
flashed for years but has been working fine.
No new peripherals for years either.

Regards KevH

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October 16, 2009 at 09:20:30
A bad CMOS battery will not prevent a system from booting. In fact, if you're not concerned about retaining the BIOS settings in memory, a battery's not even necessary...a system will boot & run without one. My guess is your problem lies elsewhere. Failing power supply?

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October 16, 2009 at 09:55:21
Thanks for your reply, jam.

I had contemplated power supply before the battery but it's just odd that the second boot will work forever...and that a battery did sort it briefly.

I note your comments about the battery not preventing the PC from booting. This is variously stated and also equally contradicted online. But, incidentally, I had another old PC fail to boot, this time before POST - it didn't switch off, but stayed in perpetual preboot state ...and a new battery sorted that one out.

computers eh!

but, yes, it could well be something else.
I'll keep power supply in mind


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October 16, 2009 at 10:04:11
I would also suspect a failing power supply; it's possibly not giving the "power good" signal at the right time.

If it's necessary to hit the reset button one or more times to get the machine to post, a new psu is usually the fix.


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October 16, 2009 at 10:19:19
Hi Skip, thanks.

Ok, still possibly a power issue.
The 'power good' test is not unfamiliar to me, so plausible .

...Though getting to POST is not an issue.

If it adds any further clues, once this first boot issue has occurred, mains power has to be disconnected and then reconnected before the second boot works. Simply pressing the on button will not activate it.

This too is not unfamiliar - from a PC building course years ago...but it's meaning is long lost to me.

maybe 'halt on all errors' or 'status after power failure' needs


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