The PSU you borrowed from the 8400, was it known working in the other computer - if so that would eliminate the PSU as your problem.
The refurbished motherboard doesn't even give you the same results as the original Motherboard(no amber light)
This leads me to believe your refurbished motherboard is DOA (Dead on Arrival) and I would contact whoever you bought it from to have it RMAd for a good working motherboard.
If the motherboard was not the problem you should at least get the same problems you got with the other motherboard (solid amber light)
Edited by thefr34k, 14 December 2011 - 10:58 AM.