Miller syncrowave 300 no power light and no weld power however have 480v input fan runs and can hear gas start when foot petal pushed

The first thing to check would be to see if you have open circuit voltage at the weld output terminals when you push the pedal. Make sure the high frequency is off if you are going to to check with a multimeter. After that if you do have OCV but no high frequency to start the arc, try it in start and in continuous. When you put it in continuous it bypasses a control relay. Also check the HF points to make sure they are clean and gapped to about ten thousandths.