When you took them apart, did anyone change or disconnect the computer's power on button from the mobo?  You need to see if those wires are properly connected in each machine.  If they are not correctly connected you will not be able to turn the machine on.  If you have the mobo manual you'll be able to see the positive and negative posts for the connection. I had this same problem, and all that was wrong is that I had incorrectly plugged the power button wires, the HDD LED wires, to the mobo.  The mobo appeared completely dead except the fans worked.  These are ATX mobos and ATX power supplies, right?

>Tom,
>
>The computers were originally networked. We have had them apart now, and I
>find I am able to fire up the power supplies by connecting pin 14 to pin 15
>on the ATX Power supply connectors. The machines still will not boot at all.
>There is no post, and the ONLY LED that lights is the one mounted on the
>mother board. We have come to the conclusion that we have all eight mother
>boards dead. The machines do not turn on any of the front panel lights at
>all.
>
>If the machines would work at all, we could reinstall the OS, but with no
>response at all, we are dead in the water.
>
>When I got the power supply working on Saturday, a quick check told me I had
>proper power from all leads, but still a dead board. When checked, the Power
>On lead had 4 volts, but when connected to a ground lead, the power supply
>immediately came alive. Still no lights on the front panel, no post. The CPU
>fan started running immediately. Nothing else I could see.
>
> What could possibly cause that, and in multiple machines? What are the
>possibilities of a run of bad mother boards?
>> ----------
>>
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