Electrical Complete Electrical Power Loss

Holy :poo:e! I am an effing idiot.
It was the negative battery cable clamp. I had replaced it some time ago because the original was shot and it never occurred to me to check it.
I discovered my mistake when I was disconnecting the battery. I had left the door open with the key in the ignition and the door alarm started chiming when I moved the negative cable.
I cleaned the connection up and put it back together and now it cranks over like a champ.
Still won't start, though.