Our receiver (pioneer vsx-405) will not power on. Push the power button once and you get the power stand by light coming on but when you hit the button again the stand by light goes off and nothing comes on.

Hello,

Usually a fault like the you ask will indicate a bad transistor in the amplification section. I suspect that the control circuit is sensing a fluctuation in the power supply and going in to protect mode. (assuming that the protect circuit itself is working properly) If a voltage is too high the unit will go in to protect mode to prevent damage to the speakers and the rest of the unit. I would take the unit in to a local repair shop and get a estimate of repair charges. Expect a 60 to 80 dollar repair charge depending on how many parts need to be replaced and what the repair labor rate is in your area.
Good luck...