The power supply system is three components - PSU,
motherboard controller, and power switch. One gets the
essential (and so inexpensive) 3.5 digit multimeter to learn
from these procedures. Even if procedures don't tell you what
is wrong, the facts provided now means others can provide
assistance. Even swapping the power supply did not tell us
much useful information: "Computer doesnt start at all" in
alt.comp.hardware on 10 Jan 2004 at
http://tinyurl.com/2t69q and
"I think my power supply is dead" in alt.comp.hardware on 5
Feb 2004 at
http://www.tinyurl.com/2musa

Was the power supply dead? Without removing anything, that
meter could have reported same in seconds. Important voltages
for you will include Power OK and Power On. What do these do
as you try to power on system. Also if the essential 3.3, 5,
and 12 do not even attempt to power, then other voltages will
be shutdown. Again, how the voltages behave is important.

Lets not forget the lockout circuit found in that power
supply controller. Completely remove power cord from wall to
reset that lockout circuit. Again, you will be wasting time
and effort without the meter. So ubiquitous as to be even
sold in Home Depot, Sears, Lowes, and Radio Shack.

chris wrote:
Thanks for the advice Dave -
I have since investigated further and after dismantling the case
and got access to the switches found that by pressing the power on
switch directly ( i.e. not via the external case buttons) the power
on LED flickers briefly and then goes out - if I repeat the process
the light doesn't even flicker with the power remaining connected -
(and the Pc doesn't acutally power up) . I have swapped the PSU and
lead with a known working one and the same happens - thus ruling
out any PSU issues.
In summary the power on LED only lights after the power has been
connected for the first time and the PC doesn't power up -
subsequent power on attmepts don't even result in the LEd
flicerking unless the power supply is disconnected and reconnected.

At first I susepcted a blown fuse but the this appears not to be
the case as the process is repeatable.

Do you think this might be a switch problem or something more
fundamental ? - unfortunately I don't know the background to this
PC ( why it was being discarded) but it seems worth saving i.e.
PII processor full set of memory and a reasonable hard drive)

Thanks
Chris