In message 8, Boris
writes:
[]
I wonder if the power supply is flakey, but I doubt it because the
machine will stay on overnight if I don't do something to cause a shut
down.

That was my thought too, and still seems possible. The bad caps one also
sounds like worth checking.

THIS IS WHAT HAPPENS WHEN THE MACHINE "SHUTS DOWN"

This is not a normal shut down. The machine doesn't give me a BSOD or
lock up when it shuts down, What happens is that the monitor goes black,
which indicates no incoming signal from pc, and the keyboard lights go
off. Both the processor and power supply stay on, and the green light
on the motherboard stays on. The network light (amber) stays on.
Again, all of this indicates no signal to peripherals, even though
everything indicates the machine is on. If this was just a video
problem, I'd expect the keyboard lights to stay on. Hmmm...if there's a
CD in the CD ROM, I can't open the CD ROM.

_Sounds_ like it's going into one of the sleep modes. Something that'd
be interesting to know is what happens to any sound that's playing: get
hold of some long .mp3 or .wav file, and set it playing soon after the
machine starts, while you do other things. I'm not sure what it would
tell us, but it'd be interesting to know if it continues or stops when
the shutdown happens. If it does carry on, then try a shorter file but
set to repeat (older versions of WinAmp have a repeat function; I don't
know if modern ones, or even just Windows Media Player, do), and see if
it repeats when it gets to the end.

The hard drive indicator light stays solid green, and doesn't blink with
activity. By the way, it never shows activity, even when I can hear
activity during file copying.

I've seen systems that have that symptom. On those, the lights on the
individual drives did show activity as normal. (I'm not sure if modern
drives _have_ such an LED on them - certainly you'd have to operate the
system with the cover off to see them, if they do.)

The green light on the motherboard stays green. The power supply fan
spins, and I can feel the hard drive is on, but hear no head movement.

During POST, the front panel diagnostic lights blink out the numbers,
but don't stay light once POST is done.

There are no suspicious logs in the event log.

Have you tried any other OSs - a DOS boot floppy, for example, or maybe
one of those Linuxes you can run from the CD?
[]
I was just letting the machine auto download more auto updates, and it
shut down. I didn't touch it.

I was also just able to install Belarc Advisor from a USB drive, and it
did it's analysis, but when I went to maximize the results window, it
shut down. I just rebooted, clicked off the Belarc analysis again, and
when it was presented on screen, I was able this time to maximize.

(You can always transfer the Belarc result file to another machine to
look at it; it's mainly just a plain HTML file.)

Has the machine ever entered this shutdown condition when you're not
doing anything? (I. e. not downloading updates, or anything.) Though
with modern OSs it's rarely not doing _anything_.

I suspect thewrong chipset/video driver. I've tried the one that came
with the Dell CD, and two different ones that show up for my service
tag, each time on a clean OS install.

I _thought_ at least one of the safe modes (and you say the problem is
still there in all of them) used a basic default driver.

This one's really got me.
.
It does sound like a doozy! I think the power supply or duff caps seem
the most likely; if you've got another power supply you can try, that's
an easy check.

(Guys, were the duff caps surface mount or through-hole? Or both?)
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

Imagine a world with no hypothetical situations...