Spontaneous Reboots, No BSOD

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My homebuilt PC often reboots itself.  I've unchecked the box for
Automatically restart in Startup and Recovery in Windows XP but still it
just reboots with no error message.  The system specs:

Abit UL8 motherboard
Athlon 64 3200
Kingston ValueRam 512 x 2
MSI 6600GT AGP video
Antec 350W PS
Sound Blaster Live! Value
Memory card reader (USB)
Samsung DVD ROM
Lite On DVD burner

I've resetted the memory and PS connections to the mobo.  Memtest 86 does
not show any errors. Nor does the Abit system testing utility (no
overheating, PSU voltages OK).  I've tried one memory stick, then the other,
alone. No dice.  If I press on the memory modules with the computer running,
it will reboot.  It seems more likely to do it during ordinary usage if I
have a memory card in the reader, or if I'm backing up to my USB external
hard drive.

Any ideas what to check next?

Re: Spontaneous Reboots, No BSOD

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Check the Event Viewer for errors/warnings.

Re: Spontaneous Reboots, No BSOD

On Sun, 17 Feb 2008 12:25:41 -0800, "WaterWatcher"

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It seems odd that it coincides with using a memory card or
USB external drive AND when you press on the memory modules.
I'd wonder if these might be unrelated.  You might take the
memory out, inspect the contacts on it and in the slot as
much as possible.  

How long since the system was built, how long has it ran in
it's present configuration (without opening the case to
change anything nor clean out dust, etc)?   We don't know if
it had formerly ran ok without any changes or if it has
developed this problem later.

Try leaving it sitting in a bios menu page to see if it also
reboots then.  Is it possible the reboot coincides with some
software?  I have rarely come upon bad driver-software
combinations where the software actually causes the hard
drive to spin down then whole system resets and it spins up
and boots again.

If it does reset/reboot while sitting in the bios, (not
pressing on the memory, just leaving it sitting there
running) I would suspect the power supply or motherboard but
with such a brief intermittent problem it'd be hard to
troubleshoot without swapping in some known good parts.

You might also check for common problems like failed fans,
unplug the PSU connectors to the board and inspect the
contacts for malformation, discoloration, etc.

Without any other leads I would begin to suspect the board
either has a crack in it, cold solder joint(s) on something,
or less likely it might have has grown some tin wiskers that
are shorting a couple of component leads momentarily.

For good measure I'd also pull the psu, leaving it unplugged
then take the top off and inspect for any burnt components
or vented capacitors.  Some Antecs are known to have
capacitors prone to failure.  If all else fails I would buy
a board and PSU from someplace with  good return policy and
send back whichever you don't need... or you could buy one
or the other at a time but  it'll take longer to resolve the
problem.  If you go that route you might also go ahead and
pull the board, PSU, etc out of the case and put them on a
desk to see if they also reboot outside of the case.

Re: Spontaneous Reboots, No BSOD

WaterWatcher wrote:
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Badly mounted MB? Possibly shorting out to (or in spite of) the
standoffs) If you run the system "bare" (out of the case sitting on an
insulating surface does it display the same sort of behavior?

John McGaw
[Knoxville, TN, USA]

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