I have two computers (one HP, one Dell)  that will not power on.  The 
Dell suffered from some lightning effect, but nothing obvious.  The HP 
went thru a series of "freezes" (HP Toast? update) before a freeze 
during flashing the BIOS killed it. Both power supplies test good, all 
voltages present and the PS fan runs when plugged into the tester.  When 
I plug the PS back into the motherboard and press the Power on" switch, 
nothing happens on the Dell.  On the HP, the CPU fan comes on but not 
the PS fan. +5v is present on both units since the mobo LEDs are on.
The power switch on the HP does close when pressed as checked by 
ohmmeter.  Didn't check the Dell.  All cables are in place on both units 
and not damaged. I thought the power was turned on by the momentary 
ground applied from the power switch to the "Power Good" line (pin 8 on 
the 20 pin power connector) to the PS.    It appears the power supplies 
are good, but something isn't working. I did try a new PS on the Dell, 
same result.
I must be missing some step in this analysis. But I'm trying to figure 
out what failed.

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