No electrical nothing and battery is fully charged

Drove home the other night everything ran fine, turned car off and went inside. Came out next day to drive and nothing, no electrical nothing. Battery is fully charged. So I changed out the starter, positive and negative wires, ignition switch and key switch, still nothing except for a hum through the speakers when the battery is hooked up, if I turn the ignition key to on the hum stops, also will change pitch if I try to turn on the headlights. Other than the hum nothing electrical.