Strange Mac Pro Issue

[128kmacintosh]

My new Mac pro has a weird issue. It's a mac pro 1.1 btw On start up it will only show a black screen.
The Diagnostic test only shows two LED's LED2, the Yellow LED (power supply is providing trickle power) and LED8 (power good). Supposedly it starts normal with a USB stick and OS on it. Which makes me think it may not be the Mother board, but maybe a Power Supply issue. Maybe it craps out upon start up???

Also, another odd thing I noticed is, when the power cord is plugged in, the computer will turn right on, without pressing the power button. My other mac pro doesn't do that. Maybe that is another hint?
Thanks everyone for your help in advance

 

[128kmacintosh]

So I took the disk drive cage out and checked for power at the IDE power supply.
on one side I get 12v but on the other I only get 2 volts and some change, It should be 5v, I think. Any other way to test the power supply? or what could be causing that voltage drop?

 

[128kmacintosh]

I u guess nobody had this issue before, huh?

 

[128kmacintosh]

So I bought a new power supply.
I changed out the front power board. But the problem still persists.
Computer runs fine when booted from USB , but none of the HDD or Disk Drive or standard graphic card will be recognized.
Is there a way to test the motherboard in Snow leopard? or something online?
I bought a new motherboard, but I still would like to know what causes the problem.