I am assembling the following new components:

Tyan S5396
Antec TruPower Quattro 1000 watt ps
Intel 5440 Xeon Quad Core x 2 with copper heatsink & fans
Crucial 2GB x 4
nVidia Quadro 3700
Seagate SAS 450GB &Seagate SAS 300GB in non-raid configuration
Windows Vista 64-bit

The 24-pin EPS PWR1, 8-pin EPS PWRCPU, 4-pin PWR2 and PW2 molex power are
all connected. When the machine is first started, fans turn on max. but no
post. Let it run for a while, eventually push power button on front of case
and turn machine off. Turn power back on after several seconds and
everything works - post, video, fans slow down, install OS & apps, Microsoft
restarts, everything fine. Turn machine completely off through Windows
shutdown command, turn on immediately and it works.

But then wait 15 minutes, machine now cold, try again and no post. Turn
power off from front panel power switch, turn back on immediately and it
works.

I've isolated the CPUs, taken the mb out of the case four times, removed the
video card, then memory, still the same.

This is actually the second S5396 I've had that exhibits this behaviour - I
RMA'd the first one and this is the new replacement that does the same
thing. Not sure what's wrong - maybe it's the power supply? All the
components seem to test okay.

Any assistance is appreciated.