p4p800d boot problems

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 Hi!  I have two of these boards (p4p800d) and I have 3 cpu's that
fit.  Board  A will  post with any of the chips.  The other (B) will
only post with the smallest chip.  The chips are 1.7, 2.8c, and 3.2e.
I flashed both boards with the 10.19 bios.  
  I have changed the PS on board B.  I've unplugged all the hardware
but the cpu, memory, and vid card.  I've pulled the battery and set
the jumpers for 10 seconds. I've switched the memory around, tried
just one stick, reseated the vid card, etc. Tried different heat
sinks. Booted with INS depressed.   All the troubleshooting things I
could think of. No beeps, no vid. no voice saying "overclock has
failed".  Just fans going and drives making noise.  
  The 2.8 was in board B overclocked to a 247 fsb and had been stable
and happy all winter.  I left it raytracing while I was at work on the
first hot day of spring and no air conditioning,  and the cpu got hot
and the machine shut down.  When I got home it booted but got hot
after a while and shut down again before I caught it on cpu-z temp
monitor.  After that it wouldn't boot the 2.8 chip but when I switched
to the 1.7 no problems. So I put the 2.8 on the other board and went
   (As a side note the new bios helped the 2.8 go from a best stable
rendering  oc at 247 fsb at  5/4 to a 250fsb 1:1 with stock vcore and
vdimm. All I did was flash the bios.  And all I do with that machine
is render in Bryce which uses 100 cpu 24/7! So it is working very
hard, but it is stable so far. With a Artic Cooling Freezer 4 on it
now it rarely goes over 42 degrees)
 Last week I got a Prescott 3.2 and tried it in board B with the new
bios but the board wouldn't post with it.  Moved it to board A and it
works fine. Put the 2.8 back in board B and it still won't post. Only
the 1.7 will work in board B.
  Anyone with ideas of how overheating would cause the board to only
see the slower cpu?  A voltage issue?  I have 400 w PS's. The heating
episode didn't seem to hurt the 2.8 chip at all.  I'm wondering if the
AGP is not getting the voltage it needs to power the vid card?
 Thanks for any thoughts, T
Tony Waterer

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