No power

I have a dual xeon system with LGA 771 sockets that went dead. I figured, it must be a power supply, so I swapped the ps and I still has no power. I tested both power supplies on another system and it showed the original ps was dead and the replacement was good -- at least the power supply itself energized -- LED on, fan on, cpu heatsink fan on. I ordered another compatible mother board -- an ASUS, vs. the original Super Micro. Same problem with new mother board and 2 new power supplies. When I turn on the ps, the "power led" on the mobo turns on, seemingly indicating power ok to mobo. I connected the power switch, held it dodn, tried reset button, shorted out the switch with a screwdriver, swapped hd's, removed fb dimm. Tried with each of 2 cpu's or both, with fans and without. No matter what I do, the only thing that turns on is the tiny LED on the mobo consistently. Any suggestions? Thanks

Actually, I replaced the mobo and the power supply and have the same problem. The only other parts to replace are the memory and the cpu's, but I don't see how they can be the problem because I removed them and I still get no power. Shouldn't the power supply at least power up with no cpu and memory?