Depending on the function of the lights, I don't see why not.
Do the diagnostic lights change if you boot this way?
Ummm, holding down the power button does nothing but make your finger tired. I don't know where holding down the button for anything came from, but it does nothing. It is a persistent, but false rumor that holding down the power button with ATX power supplies does something. The circuit is a "momentary" circuit.
you should be draining the flea power (unplug the power cable, hold down the power button for 15 seconds to drain the extra power).
Once the button is pushed (pins shorted), the circuit is ignored until pressed again.
Hmmm, then I would suspect something is getting hot. Have you inspected for leaky capacitors?
Now, when all I have connected is the mobo and one stick of ram, I get all green lights---then it shuts down after being on the same amount of time as before.