Dell T7400 3.0Ghz CPUx2, 750gb SATA x2. 16Gb (2gb x8)

The unit was started today, with the intention of testing some
SAS Drives. (the side panel is open) I installed a LSI 3080x
PCI-X SAS Controller, the bios saw the card and I was able to confirm
that 2 of the 4 drives I had tested ok. When I came back into the
room, I noticed a blank screen, thinking that I forgot to power on the
system in order to test the 3rd drive, I pressed the power button, and
the system did not power on, there was  a low power on noise, and the
front panel displayed # 1-3, while the power button slowly flashed yellow

I downloaded some dell doc's, and determined that 1-3 are power related
problems, I followed the instructions, disconnecting each powered device
(video card, sata drives, and 2 dvd drives). there was no effect to the power
problem.  I then removed the motherbrd power connection (power-1) and
the unit literally sounded like a normal boot, all fans spun up. I also
tested the power supply by pushing the small test button on the back
the LED came up green. Based on the information in the dell doc's
it would seem that the power supply is OK, but that the MB is the problem

The yellow LED on the Mb is on when the ac cord is inserted. There is no video
being displayed( tested 2 different cards)   Would you agree that the MB is the problem