Did you use an inverter on the soft-power-on wire? Of the ATX and old style Mac power supplies, one of them uses 5V as the power-on signal and the other uses GND as the power-on signal. I can't remember which is which, but you need an inverter on that wire to make it work, if you switch from one to the other.You're really going to want to convert it to ATX. It's so easy even I could do it. I couldn't get the soft power to work, though.