XPS 210 won't start up

I have an xps 210 that quit working.  When I press the power button I get get an amber flashing light on the button.  I get no diagnostic lights.  I replaced the CPU cooling fan with no change.  I replaced the mother board with no change.  I unplugged each component, hard drive, DVD, USB port, one at a time with no change.  The lack of diagnostic lights points to a pre bios problem.  When it first tries to power up the hard drive cooling fan and the power supply fan both start to move and then quit.  I jumpered the proper pins on the power supply to make it start and got the correct voltages on the ATA cable.   I suspect the power supply, but not sure.  I will end up buying a complete new unit one part at a  time at the rate I am going.  Any ideas?