Well, I not sure his explanation is too clear, and it is definitely not true for all boards. It is a design issue with the board / product, but not necessary a problem.
When you apply AC power , stand-by power is what comes on ( I assume this is what he means by remote power)
The stand-by power operates a limited number of circuits on the mother board that deal with the power control and features that should work whether you system is on or off (like wake on lan, or PCI card wake)
(SIDE NOTE: because stand-by power is present in many parts of the board when you system is "off" you should always unplug the power supply before attempting to install or remove any components. This is one place a lot of folks manage to kill their systems by plugging in stuff with the (stand-by) power connected)
In the best hardware designs, the circuits should be configured so that everything stays off until told to power-on. However, many Hardware designer don't think about the possible race conditions on first power-up and fan jumps or on\off events can occur.
Many boards also have settings in BIOS set-up to define how the board is suppose to react to an AC power event. (Stay off, Turn on or Last State)
Stay off and Turn On are self explanatory, but Last State means that if it was on when the AC was removed it should turn on when AC is reapplied.
Some factories may just pull the plug when they finish building and testing so the first AC at the customer , the system powers on.
With Intel high end boards ( I don't know desktops as well) you can press and hold the power button for 5 seconds to force a shutdown regardless if the Baseboard management controller is running or not.
As far as the your problems,
- Check the power and all the connectors. Some board require 3 or more connectors from the power supply. (The 2X4 pin - 12v to CPU is one commonly missed. which then causes the board to not POST, but the fans will run)
- Check the CPU socket. CPU sockets pins are very fragile and dropping a CPU in off center can bend them
- Make sure your memory is on the mother board's supported list and fully seated
- Remove any add-in cards and see if system will POST without them if your having troubles.
- Check all cables and wiring. Unplug anything not need to POST if your having troubles. Shorted USB plugs or Front panels missed wired can cause real headaches trying to debug.
"Both boards were tested and fully working when they left here" would kind of worry me. Why would a distrubutor open the ESD seal on a new board to test it and risk damaging it when it was tested by DELL before they got it, unless it was not a new board?