My power down/power up procedure in Vista 32 goes as so:
1. Power down in Vista. Computer appears to power down normally (monitor loses signal, drives stop spinning, etc) except fans and USB devices stay on.
2. Holding in the power button doesn't shut the system down at this point. I must turn off the switch on the power supply to shut down everything.
3. Turn on the power supply switch. Push the power button on the tower. Fans & USB come on; computer does not.
4. Hold in the power button. Everything powers down. Hit the power button again, and everything powers up like it should, and I go into Vista with no problems.
I'm using a P5N32-E SLI mb.